I have a fairly simple question:
I'm currently at odds with Arabia, and I'm interested in invading them, but they have several sllies I'd rather not have to go to war with as well. is there an easy way to get him to declare war on me?

Your target will drag his/her friends in the war even if you did not start the war. You can make his friends busy (dragging them into other wars) before declaring the war yourself.

If they're allies, I believe they attack regardless. If it's defensive pacts, you can try making repeated outrageous demands to get him to declare. The AI may still declare anyway, but I'm not sure how that plays out.

to clarify, they do have defensive pacts. I was thinking about trying to sabotage something with a spy

To get him to declare war on you, make him angry with you, and eliminate some of your troops. If the AI notices your power chart dropping, it will see you as an easy pray, and attack, regardless of defensive pacts.

The downside is obvious, other foes will show up and attempt to get some of your precious cities, and since you'll have less troops, it'll be harder to defend yourself.

I've found myself in that situation before: multiple AIs with mutual defense pacts. If I declared on my target, all of them would attack. I was able to limit the damage by carefully checking the web of defense pacts. I found one AI (Monty, of all people) who only had one DP -- that being with my target (Genghis). I declared war on Monty, even though he wasn't in my plans at all, causing the DP with Genghis to activate. That caused Genghis' other three DPs to be cancelled, and I only had to fight those two at first. Genghis did eventually end up dragging Alex into it just before suing for peace.

i had a symilar situation i needed to declare war on cyrus but hatty had a defensive pact with him. luckily i had a good relationship with hatty so got her to declare war on alexander then attacked cyrus and hatty didn't decalre war (don't know if thats suppose to happen) i also was able to get everyone else to declare war on cyrus to.

I find the easiest way to break up defensive pacts is to get one of them to declare war on someone else, though it won't work if both civs are peacemongers, because the others value the defensive pact more. That's how I got Louis XVI to come out of his defensive pact, he declared war on Saladin then I marched in and destroyed him, gaining the land I needed for a domination victory.