Physical appearances (gotta find them attractive) aside, intelligence. I don't mean that in the "you must have some sort of degree;" not as in book smarts, just the ability to hold an intelligent conversation. If I'm rolling my eyes uncontrollably, it isn't going to work out. I don't care if our thoughts on every matter are polar opposite, I can deal with that, but not being able to elaborate on why you hold that opinion? Not being able to hold a rational discussion on a topic? Or even worse, attempting, failing, then getting really angry/upset at this fact? Assuming I'm insulting you or intentionally trying to piss you off by calmly discussing something? That just annoys me to no end and locked in a room for long enough, I can guarantee only one of us is gonna make it out alive. It's handy at times though, the reason I couldn't date someone too young for my age has nothing to do with legality - though it is naturally a convincing argument - but because I'd end up punching you in the face before we got to that stage (hyperbole, in case anyone ends up on a 'abuse of women' rant).
On the flip side is the ability to actually have fun, and have it independently. I'm not going to choose between you and my friends but you're often more than welcome to join me when I'm with them; I AM going to go out without you and I expect you'll probably do the same. I like my "me" time as well, don't be offended by that fact. You have friends too, I don't need to be present every time you spend time with them. Nor do I need a blow by blow account of your night out, have a good time, I trust you, put down the damn phone and enjoy yourself. A little bit of crazy is a good thing, in a long term relationship the last thing I want is for things to become boring. I went out with a girl at uni and it's only after we split up that I realised how much I'd been 'reigned in' in terms of going out and usual activity. She didn't drink so never wanted to go out so we'd always end up at the theatre or for a meal by ourselves, which don't get me wrong, I do enjoy doing, but it's good to balance that with letting your hair down and just going out and having a laugh with friends from time to time.
Just about everything else I can deal with. Tattoo's? Awesome (to a point). Vegetarian? Just don't shove it down my throat when I'm biting into the side of a pig. Religion? Well, that satisfies the "crazy" criteria, just don't expect me to convert any time soon. Even personal hygiene to a point, mines DREADFUL, but if it's getting to the 'physical attractiveness' issue then obviously you've gone too far and it's time to take a damn shower. It all boils down to acceptance and compromise, I'm not perfect and neither are you. Deal with it.