When's a time you've seen 'banter' take a nasty turn?

There are two things really. Sometimes it just isn't banter and is just conversational prelude to an inevitable battering or a swedge. I have rarely seen genuine banter descend into chaos without either prior bad blood or a tacit intention to look for and provoke bother. I mean, on any given night out, you will see the eyeballing 'you looking at me?' brigade knock out banter or 'friendly' conversation that is really designed to insert an opening to either take or cause offence in order to descend into physical violence. I've seen that plenty on nights out. I have a friend who is quite tall (about 6'5") but was also an utter bean pole until well into his thirties. Unfortunately, although he is a lovely friendly chap, this made him quite the target for wankers looking for a scrap as either a) they can claim they fell a giant or b) he smacks them about and they can claim he was a massive bloke and it wasn't a fair fight etc. I saw on many occasions these knobheads would start off with a crack that appeared to be banter (*'nice shirt mate, do they make them for men?*') and however he responded they would either take offence at a witty retort or even take offence that he didn't take offence.