I'm tolerant to a lot of different outlooks but some people give off this ooze of nastiness where everything they say is tinged with bile, and they just have to be mean and sarcastic and negative. :( I'm like an emotional sponge so it just leaches into me, it's awful. They're the kind of people who make a hobby of it almost (I've known a few who will just sit in public places and make horrid comments at strangers). These kinds of people are usually very narcissistic as well and don't seem to realise that their revolting attitude is just reflecting back at them and making them the ugly ones.
Also, people who wish harm on others or joke about traumatic subjects. That is something that makes me really angry. I have to step away when I see/hear it because otherwise I'll get emotionally involved and that never works out for me.
This goes without saying but creepy people I avoid like the plague, especially incel-types lol. Even "mild" incels are extremely unsettling.
People who have you on rotation because they want something out of you, and if you're not available you KNOW they're just doing it to the next person, then the next. In other words, using you, never actually wanting to know you.
When people hate animals and/or children and old people, I find that hard to listen to, but depends on the individual and how bad it is. Prejudice of all kinds really upsets me but ageism is definitely up there and I feel like it's encouraged these days.
Disparaging and dismissing others for their looks is just... a huge no.
As mentioned in this thread, being told what I think and feel, or what I SHOULD be like, is a surefire way to infuriate me!
I cannot really handle judgemental / controlling / confrontational personalities.
tl;dr what Gardevoir said, pretty much just bullies that come in all shapes and sizes.