Well if you're dead? That's a deal breaker, I don't date dead people.
If you're a dude? That's a deal breaker, I'm straight, sorry.
If you're a child? Also a deal breaker, I ain't a paedophile either.
If you're not a member of the human species? Deal breaker... But then how are you reading this in the first place? I should probably be asking this about the dead people too though. :/
Though you probably want some serious answers, don't you? :P
Note, I'm going to skip the really obvious ones like being abusive, doesn't care about you etc.
Also note, I'm focusing strictly on romantic relationships. Since with friendships I can tolerate almost everything to some extent, since I'm not going to have to live with them or anything and get to have plenty of time to myself.
1. Easily Triggered/Offended
Dark Humour, Bluntness, Challenging ideas and beliefs, these are all things I consistently do or engage in. Someone whose quick to throw a fit at these things isn't going to last long, at all.
2. Dishonest
I don't even mean in the cheating way. I mean even if they're the kind of person who follows sayings like "If you got nothing nice to say, say nothing at all", or "It's better to tell a happy lie than a painful truth". Because suddenly I have no idea if what you're telling me is true or not, which completely destroys our foundation of trust if I've always got to be questioning what you're telling me is true or not, even if the intentions are good.
3. Prioritises Money & Status over Family & Personal Life
I've become pretty confident in that even though I don't know what route my life will take me in, it's going to be a route that priorities my ability to learn, see friends, enjoy hobbies, spend time with my (hopefully) future partner and children etc. Someone having a High Demanding Career they care a lot about is highly respectable IF the career involves helping people and/or fighting for a cause, and although that might put a strain on our relationship, I could be willing to make it work. But if their Career is more focused on just making money, getting promotions, and making more money? And increasing their wealth and status becomes their primary goal in life? I want no part in it.
4. Jealous/Controlling
I feel I should clarify here at the start I do NOT mean clingy. I actually don't mind clingy, I like feeling like I'm cared for, missed, needed etc. Rather what I'm talking about are the people who don't want their partners to have a social life. Like, although my circle of friends isn't particularly large (Like, 12 people IRL, a few more online) I still have other people I care about and enjoy spending time with, people who I would of known longer than anyone I end up dating or marrying. I'm not going to cut them out of my life cause my partner can't handle me enjoying the company of people other than them. Like, seeing my friends less often? That's to be expected, that's just math and time with everyone having jobs, their own families to see, me spending quality time with my own partner and kids etc. But when something does come up, unless if there's a good reason for it I don't want my partner to be telling me not to go.
I debated removing this one cause I figured it counted as being an obvious one. But there's enough people who seem perfectly comfortable isolating themselves to just their partner after a marriage that I figured it should still be stated.
5. Parents as an Authoritarian
I very much plan to raise my future children to be free and independent thinkers, to examine the evidence, challenge ideas, question authority etc. So having a Partner who simply plans to spill their personal agenda onto our children, and turn them into clones of themselves? Nu-uh... Doesn't even matter if I agree with what you're telling them to think, the issue is that you're telling them what to think, and not teaching them how to think.