People who aren't careful with their words, not realising how rude they actually being.
I recently got raged when my friend ignored me after saying something to me. Didn't realise I got angry till my friend told me.
People that gotta be correct all the time, you know that one stubborn guy, that will argue just about anything (Opinion-based) for the satisfaction of being right.
I instantly rage out when I have to listen to people eating with their mouths open. Listening to their lips smack, or listening to them try and keep the food from falling out of their open mouth. Seeing my cousin has a 50/50 chance of sending me off the deep end, it really depends on if I am prepared for it or not.
I'm a pretty punctual person, and I often leave and arrive early. I hate it when I want to do something and I'm waiting on someone else who is meandering around the house and taking their sweet ass time. I like to have a plan, and do things and not piss around all day trying to get going. So I guess I hate waiting for people who are completely inconsiderate of plans/time.