Here is a list of some of the things I have learned in my life... pretty much all by (unfortunate) experience - mine or someone close to me. I can laugh about most of them now - or at least not cry about them. =)
Spilled cat litter (or litter kicked out of the pan by the cat) is easier to sweep up when it's dry than when it's wet (from the overflowing washing machine drain). Wet clay cat litter is really just mud.
If you have a basement with a sump pump, a high-water alarm is a good idea, and so is a back-up sump pump. If you are gone away, be sure you have someone who can check on your house (including basement) if there is any reason to think the power might have gone out (like a storm).
A tidy basement is easier to mop up than an untidy one.
Throwing away a soaking wet mess (papers, toys, junk, rugs, etc.) from the basement is hard work, exhausting, and makes additional mess on the stairs and out the door.
The rubber hoses leading to the washing machine don't last forever. Make a habit of checking them regularly. If you see a bulge, turn off the water, and get the hose replaced ASAP.
A washing machine hose can burst at any time, whether or not the washer is running.
Hot water spraying from a burst washing machine hose causes a nice warm rain to come down from the ceiling.
Opening the door to a warm rain inside the house is not an indicator that you'll be having a good day.
A tall person (say 6' 4") can dry an 8' ceiling without needing a stool or ladder.
Unopened paper towels will still soak up water if they are sitting in it.
A light on a fish tank can catch fire if the water splashes up onto it and seeps inside. (First response - unplug it, DON'T touch it until the power is off!!)
Water dripped onto a power strip or extension cord can cause a fire.
Burned plastic stinks, and makes a hazy smoke.
Circuit breakers are home-saving, life-saving friends!
Before leaving on vacation, if you are going to shut the cat out of the bedroom, make sure he is OUT of the bedroom when you close the door.
A cat cannot hold his bladder nor his bowels for 3 days when shut away from the litter box, say, in the bedroom. Blankets on the bed make an acceptable (to the cat) substitute. (ugh)
If you drop a new plastic jug of milk onto a concrete floor, it will split open.
A gallon of milk makes a very large puddle.
Never open the door for the cat when he is holding an animal you think is dead. You might be wrong.
Frightened baby rabbits can fit through a very narrow hole between boards under the cupboard, even if you didn't know the hole existed.
Slippers that are actually slippery are very dangerous, especially on stairs.
Even if a person has a fairly cushiony bum, it won't prevent back injuries if you slip and fall on said bum. (ouch)
If you bend a stick away from your face in order to break it, don't be surprised when the broken stick snaps you in the nose. (ouch again)
Always remember... gravity isn't just a good idea, it's the law. You will obey. Things above you will obey, too.
Even if he didn't mean to drop the hammer onto your arm, it still hurts and makes a large bruise.
Pillows that have been thrown are very good at pruning African Violets... even if they don't need pruning.
Weed killer that gets splashed on your flowers will kill them just as well as it kills the weeds you are spraying that have sprouted between the bricks.
No matter how many times you dry all 4 of the dogs' feet when he comes in the house, he will never be able to count to 4.
Needing to use crutches for two weeks is not much fun. It's less fun if you are also tent camping during that time. And the bathroom is uphill. (honey, you are driving me to the bathroom now)
It is not easy to shower while standing on one foot, with one hand pushing the button that makes the water flow and the other hand doing the washing of your waist-length hair, and having no control over the temperature of the water, which is just too hot for comfort on a 90-degree day. (stupid campground showers!!)
When I am too hot and not very clean even after showering, I'm a little cranky.
Liquid that has reached boiling temperature but has not been stirred really does "explode" - and if it is juices from a turkey to make into gravy, it makes a greasy wet mess all over. This can happen whether using a stove or a microwave. (Thankfully, no one was near enough to be splashed and injured - it was just a greasy wet mess to clean up.)
Scissors that are sticking because they are bent should not be straightened by bare hands. They can still cut.
If someone has removed the safety guard from the paper cutter because they were cutting extra large paper, be sure it is replaced promptly.
A cut that goes through your thumbnail cannot be sewed.
Even a very mild-mannered person knows bad words, and will even say them if in enough pain.
Even a table knife can cut you, if you are pressing hard... say, hard enough to cut through a frozen stick of butter you are holding in your hand.
If you are backing your van out of the garage, be sure to check the clearance of BOTH mirrors.
If you are eating your dessert outside, and you put down the bowl in the grass because you want to go play on the swing for a few minutes, don't be surprised if the dog finishes your dessert for you.
If you are falling off your pony and have a choice between falling in the manure and falling on the watering trough, choose the manure.
Manure stinks, and it tastes bad. But it is softer than a watering trough!
Those brightly colored fur mousie cat toys will bleed their color onto the floor (or wherever) if they get wet. That stain is impossible to remove. (Buy the white or un-dyed ones.)
A 4-year old can open my clothes dryer from the outside but not from the inside. A 2-year old can't open it at all.
It is dark inside a clothes dryer when the door is shut.
I can hear the muffled screams of a 4-year old inside a (not running!) clothes dryer, even when I am at the other end of the house. (No one got hurt.)
I can run from one end of the house to the other in a matter of seconds (well, okay, I could when my kids were 4 and 2).
Both girls laugh about that one, now. They never played in the dryer again, either.
Amy
Spilled cat litter (or litter kicked out of the pan by the cat) is easier to sweep up when it's dry than when it's wet (from the overflowing washing machine drain). Wet clay cat litter is really just mud.
If you have a basement with a sump pump, a high-water alarm is a good idea, and so is a back-up sump pump. If you are gone away, be sure you have someone who can check on your house (including basement) if there is any reason to think the power might have gone out (like a storm).
A tidy basement is easier to mop up than an untidy one.
Throwing away a soaking wet mess (papers, toys, junk, rugs, etc.) from the basement is hard work, exhausting, and makes additional mess on the stairs and out the door.
The rubber hoses leading to the washing machine don't last forever. Make a habit of checking them regularly. If you see a bulge, turn off the water, and get the hose replaced ASAP.
A washing machine hose can burst at any time, whether or not the washer is running.
Hot water spraying from a burst washing machine hose causes a nice warm rain to come down from the ceiling.
Opening the door to a warm rain inside the house is not an indicator that you'll be having a good day.
A tall person (say 6' 4") can dry an 8' ceiling without needing a stool or ladder.
Unopened paper towels will still soak up water if they are sitting in it.
A light on a fish tank can catch fire if the water splashes up onto it and seeps inside. (First response - unplug it, DON'T touch it until the power is off!!)
Water dripped onto a power strip or extension cord can cause a fire.
Burned plastic stinks, and makes a hazy smoke.
Circuit breakers are home-saving, life-saving friends!
Before leaving on vacation, if you are going to shut the cat out of the bedroom, make sure he is OUT of the bedroom when you close the door.
A cat cannot hold his bladder nor his bowels for 3 days when shut away from the litter box, say, in the bedroom. Blankets on the bed make an acceptable (to the cat) substitute. (ugh)
If you drop a new plastic jug of milk onto a concrete floor, it will split open.
A gallon of milk makes a very large puddle.
Never open the door for the cat when he is holding an animal you think is dead. You might be wrong.
Frightened baby rabbits can fit through a very narrow hole between boards under the cupboard, even if you didn't know the hole existed.
Slippers that are actually slippery are very dangerous, especially on stairs.
Even if a person has a fairly cushiony bum, it won't prevent back injuries if you slip and fall on said bum. (ouch)
If you bend a stick away from your face in order to break it, don't be surprised when the broken stick snaps you in the nose. (ouch again)
Always remember... gravity isn't just a good idea, it's the law. You will obey. Things above you will obey, too.
Even if he didn't mean to drop the hammer onto your arm, it still hurts and makes a large bruise.
Pillows that have been thrown are very good at pruning African Violets... even if they don't need pruning.
Weed killer that gets splashed on your flowers will kill them just as well as it kills the weeds you are spraying that have sprouted between the bricks.
No matter how many times you dry all 4 of the dogs' feet when he comes in the house, he will never be able to count to 4.
Needing to use crutches for two weeks is not much fun. It's less fun if you are also tent camping during that time. And the bathroom is uphill. (honey, you are driving me to the bathroom now)
It is not easy to shower while standing on one foot, with one hand pushing the button that makes the water flow and the other hand doing the washing of your waist-length hair, and having no control over the temperature of the water, which is just too hot for comfort on a 90-degree day. (stupid campground showers!!)
When I am too hot and not very clean even after showering, I'm a little cranky.
Liquid that has reached boiling temperature but has not been stirred really does "explode" - and if it is juices from a turkey to make into gravy, it makes a greasy wet mess all over. This can happen whether using a stove or a microwave. (Thankfully, no one was near enough to be splashed and injured - it was just a greasy wet mess to clean up.)
Scissors that are sticking because they are bent should not be straightened by bare hands. They can still cut.
If someone has removed the safety guard from the paper cutter because they were cutting extra large paper, be sure it is replaced promptly.
A cut that goes through your thumbnail cannot be sewed.
Even a very mild-mannered person knows bad words, and will even say them if in enough pain.
Even a table knife can cut you, if you are pressing hard... say, hard enough to cut through a frozen stick of butter you are holding in your hand.
If you are backing your van out of the garage, be sure to check the clearance of BOTH mirrors.
If you are eating your dessert outside, and you put down the bowl in the grass because you want to go play on the swing for a few minutes, don't be surprised if the dog finishes your dessert for you.
If you are falling off your pony and have a choice between falling in the manure and falling on the watering trough, choose the manure.
Manure stinks, and it tastes bad. But it is softer than a watering trough!
Those brightly colored fur mousie cat toys will bleed their color onto the floor (or wherever) if they get wet. That stain is impossible to remove. (Buy the white or un-dyed ones.)
A 4-year old can open my clothes dryer from the outside but not from the inside. A 2-year old can't open it at all.
It is dark inside a clothes dryer when the door is shut.
I can hear the muffled screams of a 4-year old inside a (not running!) clothes dryer, even when I am at the other end of the house. (No one got hurt.)
I can run from one end of the house to the other in a matter of seconds (well, okay, I could when my kids were 4 and 2).
Both girls laugh about that one, now. They never played in the dryer again, either.
Amy
Most of these are great! 
But maybe this would have been better in the Humor and Jokes forum? 
Don't know, just a suggestion.
