That was a great post Kafka2, perhaps the best I've ever read in this forum!
As for my picks for the worst jobs in history...
A servant of Louis XIV in Versailles.
You have to undress and dress that man(?) every evening and morning. By chance, you might have to taste his morning tea, which is one-quarter tea, one-quarter water, and the rest perfume.
You have to spend your day with him and his surroundings, all with horribly powdered faces, you have to smell some disgusting 17th century perfume all the time (and just don't get a headache!), you have to help him on and off his horse, carry his prey from hunting excursions (and don't let the blood soak your clothes, or else!), and you might even have to wipe off his arse! But worst of all, you won't be remembered at all!
A slave of an owner of an insula in ancient Rome.
The insulae of the city of Rome were the most unsafe buildings ever constructed. Nearly every day, at least one of them caught fire or collapsed, burying every poor person underneath. As slave of the owner, you get to live in the rooms on ground level. You never get to leave the house. Living in an insula was damn dirty, loud, it stunk to hell, you would have had to take all complains of every person living there (and believe me, that's not few), tend any animal which happened to be living there, perhaps even taking care of the staircases (wooden staircases, very narrow, and, of course, not at all robust). But worst of all, if this insula decided to collapse, you're f*cked.
But the most horrible job in history, in my opinion, must have been being a slave of a slave of a slave in ancient Rome.
This indeed happened! Some owners actually gave their slaves a pay, allowing them to possess whatever property they wanted. Some slaves saved their money for so long, that they bought themselves slaves. These were called vicarii. You can imagine that admitting to be a slave didn't give you the best of reputations. But imagine admitting to be the slave of a slave!
Not enough, though. Even some of the vicarii were given a loan from their masters, the normal servi, i.e. the slaves. And it actually happened, that some of these vicarii bought their own slaves! Now imagine that you have to tell someone that you are the slave of a slave, who again is the slave of a slave!
That is, in my opinion, the most rotten existance in history.