Deal breakers are like, well, opinions. Everybody has one. Or two.
I think it's important to share this information with your significant other pretty early on, just to be fair. Ostensibly, in a new relationship, you want to give each other the best possible shot at success and knowing the other's deal breakers at least lets you know what might send you to Jail without passing Go.
I really only have one, and that is: cheating. (I want to put that in bold italics but that would give the word more power, and, wow, it is powerful enough on its own. It already has creepy organ music and thundercracks accompanying it in my head.) Cheating is like six kinds of offensive. There's the lying, of course, but worse than a web of lies is the realization that your partner doesn't want to share something with you. And worse than that is the realization that your partner doesn't want to sleep with you.
My main goal in life, as you might imagine, is to stay alive. When your significant other cheats, your health is directly threatened. Of course there's the very real, frightening possibility of contracting an STD but I'd worry more about my health being threatened by winding up on death row after murdering someone. See, nobody wants that.
One of the many things that my boyfriend and I have worked really hard on is unflinching - and sometimes brutal - honesty, and our secrets from one another are few and far between. (The secrets we do have are necessary and important to us. That's a topic for another day.) Someday he may sit me down and tell me something I don't want to hear, but I wouldn't have it any other way. He knows that he can tell me just about whatever's on his mind, and that we'll face it together. Unless, of course, what's on his mind is, "I cheated on you." In that case, would someone please gather up some bail money and get my lawyer on the phone.
My deal breaker is probably pretty common. I'm interested to hear what transgressions are on your list.