Very, very very rarely. In fact, I can only remember one single time, although I’m relatively certain that there might be one or two more…
When I was at UT: Austin I was crossing the street (at a red light) with a friend. A youngish (college age looking) girl had pulled into the pedestrian crosswalk and was busy chatting away on her cell, so we were forced to walk behind her car. Now, my friend is a hemophiliac, so getting run over by a car would’ve been a Very Bad Thing. And, of course, the girl decided that backing up rapidly, while we were a few feet from her back bumper, was a good idea. And by rapidly, I mean if she didn’t floor it, she at least put a fuck of a lot of gas into it while it was in first gear, or something.
I shoved my friend out of the way and jumped back myself to avoid getting smashed by her car. At the same time (fuck knows how I coordinated this, I was working on adrenalin) I smashed my hand into her trunk to kinda of ‘push off’ and get more distance from her bumper, while yelling something along the lines of “stop your fucking car!”
Unselfconscious, she leaned out of her window and, rather snottily said “You know, you didn’t have to punch my car!”
Without a second of thought or any doubt I responded “You dumb bitch, you nearly ran us over. If you don’t want someone to smack your car, fucking check if there are people behind you before you accelerate backwards because next time if you’re lucky it’ll just be someone suing your stupid ass instead of you killing someone. Go fuck yourself your irresponsible cunt.”
Pretty sure nearly getting run over is about my threshold to start cursing at someone in public.