In this instance, what the person said was skipping merrily over the line of polite conversation anyway. Like I said, he was trying to get a reaction, he just didn't realize the strength of the reaction he was going to get.
Pulling from a real life scenario - Buzz Aldrin. Walking up to someone like him and making harassing comments in front of his family was not in any way an acceptable thing to do. However, I doubt the person who did it realized Buzz Aldrin was going to skip over the 'get out of my face' and go directly to 'punch to the head'.
I admit, there is a part of me that wants to just sit back, make popcorn, and watch the well deserved thrashing. But since that's also the part of me that wants to key the cars of folks who park in the firelane and dump soda on the folks who talk at the theater, I tend not to trust it's decision making skills on the etiquette issue.
On the event that inspired this post, a friend broke the incoming tension by saying, 'Breath, Joe. It's way to difficult to get rid of a body when it's -10 out'. Funny...but possibly not polite. It stopped Joe for a couple seconds while the other party was more or less dragged out of the room.
I guess I don't understand people who get to the "something bad happens" point. We're adults, we should act like it. Blowing up and being threatening, etc. is not right in any situation. If you can't handle your traumatic scars, then get some help so that you aren't a danger to others if the subject comes up.
This popped up when I went to post the above...and I think requires me to elaborate a bit more.
The troll in question was joking about driving drunk. Joe was getting annoyed and said 'knock it off, that's not funny' in a very tense voice. The troll then made a comment of 'well if folks can't dodge cars they should stay off the sidewalk'. Joe's son was killed a few years ago by a drunk driver, while standing on a street corner waiting for the light to change.
IMHO, the incoming thrashing was not entirely unwarranted, but...well... violence really isn't the best answer in most cases.