I suppose it is normal, as you grow up, to develop "deal breakers" - things you can't easily tolerate in other people. I'm talking about the kinds of things that, if you saw them in someone on your first date, would keep you from having a second date. You'd just know that person wasn't right for you.
One of the things I find really difficult to deal with in other people is frequent anger and judgment of others. Sometimes I meet someone, or get to know them, and I learn that their head is filled up with lines that other people shouldn't cross - things that turn other people into idiots or assholes to them. And often these things are pretty trivial or common - faux pas, simple acts of inconsideration or inattention, that kind of thing.
Yesterday, a coworker drove a couple of us to lunch. The parking lot of our office building has a 4-way stop and another driver proceeded through it when my coworker thought it was his turn. Instead of just letting him go, my coworker cut the guy off and, though he didn't do anything directed at the other driver, he did rant about it a bit in the car, saying something like, "Fucking moron!"
My other coworker, in the backseat, said something like, "Getting a little angry at other drivers there, huh," and the driving coworker said, "I only get angry at the idiots."
Well, you know, everyone is an idiot driver sometimes. I mean, honestly, not being sure when it's your turn at a 4-way stop does not make you an idiot or a bad person. And lest it sound like I am giving my coworker a hard time over one incident, he proceeded to talk about how many idiots there are on the road, and kind of went on like that for another couple of minutes.
I guess in general I feel like if you find yourself ranting about things that are very common - for instance, if you say things like you hate to go to restaurants these days because so many people are rude in such-and-such ways - you are the one with the problem, not the world. Common events - slow drivers, people talking on their cellphones on the bus, teenage boys who wear their pants real low, people forgetting to RSVP, etc. - do not justify real anger and a bunch of complaining to whoever is stuck listening to you.
I guess I draw the line somewhere between annoyance and anger. "God, this person is slow, what the hell, DO NOT DRIVE 20 MILES PER HOUR," seems OK to me. "What a fucking idiot. GET OFF THE ROAD! I cannot STAND slow drivers. If people can't fucking drive they should just stay home," is over the line.
And yes, I do see the irony in being intolerant towards the intolerant. But I don't think they're all idiots or assholes who should be killed or forbidden to live in the same cities as normal people or anything - I just think it's an unfortunate personality trait that a person should work to improve. And I find myself pretty much unwilling to hang out with people who unabashedly display it.