I basically don't care about mistakes as long as it doesn't cause a wipe. People die all the time, and the "good" players kill themselves a lot too, trying to greed in on their parses with no consideration for anyone else.

Basically the only time I'll take issue with anybody is if somebody starts to smack talk on someone who is either performing better or isn't responsible for a mistake that had just occurred. It's more common between the tank and healer dynamic, as I don't parse, but occasionally it's DPS on DPS usually in regards to who was supposed to stand where.

A lot of times people start preemptive smack talk in order to try and veil their own incompetence, and that grinds my gears worse than anything else. If you make a mistake, own up to it. With all of the ways people have to look over fights it's unlikely that you'll get away with shifting the blame to an innocent. Those types of people I am willing to throw away a party for or kick, of course, sometimes people join up with their friends and when you kick one they all go, but oh well. That's life.