I think most people have a mental list of things they won't do in the bedroom, or wherever it is they do their fucking. I think most people mention things like blood and scat (shit) as being a definite "no" when it comes to what they're into.
I'm fairly open-minded when it comes to kinks. I don't have a lot of kinks of my own, and when asked if I'm kinky I don't really have an answer other than to ask that person what they are into. I'm usually game to at least do my best to accommodate someone else's fetishes or kinks, though I really haven't encountered too many. Most of my encounters have been one-timers, and people don't usually drag out their fetish gear for a first time meet-up.
My own deal breakers tend to be anything that puts me in a submissive position. By that, I mean anything that makes me feel submissive, or humiliated. Personally, I can be on an even playing field with my partner-of-the-moment, or be dominant, if that's what they like, but not submissive. It puts me in a weird headspace.
I won't piss on anyone. Not because I'm against it in any way. I'm just pee shy, so it just wouldn't be possible. Blood play and scat are also out of the question. Blood is not a turn-on to me, and I don't like causing longer-term bodily damage. I might slap your ass, because the welts will go away in a few hours usually. The cut could stay with you a while. And I'm just uncomfortable with that, in general.
I also am not a fan of rape fantasies unless I trust the person. I have these images of someone asking me to "rape" them and then them filing charges against me for shits and giggles. Or someone on Grindr arranging for a "rape" scene and inviting me over, only to find out I was never talking to the actual person, and the person I was talking to had sent me to someone else's house to unintentionally rape someone. I could picture that happening.
I don't mind any sort of binding or tying, or anything on that order, as long as it's not being being tied up. Same with ass slaps, and scratches, etc. You get to be the receiver, not me.
Massive amounts of leather are kind of a turn off for me. I don't know why. There's a certain leather look that looks too butch for me, and that look is unappealing to me. However, some light leather, like cuffs or a harness, or chaps, etc., aren't going to bother me, and might even be a turn on, if they're worn by the right person.
I think it's good to be open-minded to at least try some things; to help out your partner. Especially if you're like me and don't really need it to get off, but it doesn't bother you at all.
Do you have any deal breakers. or hard limits?