The guy is 70 show some respect, If you dont like the conversation sit at another table .

was it a very small bar ??? I dont see why you couldnt move somewhere else in the bar away from him,As for hitting him and thinking it is acceptable in a UK bar I can tell you now I worked doors in UK for many years and if I saw you hitting an old guy youd be out quicker than you came in,Is there is no reason you couldnt act like an adult and walk away. I meet idiots now and then I find it more fun to play along with them and laugh at them till I get bored then walk away.One further point I'd like to point out, just cause someone looks like a tough guy dont mean they are and just cause they look an easy target dont mean they are, the only way to learn that lesson is the hard way and I think you may be on the road to learning that lesson unless you relax and stop stressing about other peoples hang ups

I can't thibk what's more embarrassing,

Old guys thinking they are tough in a foreign country because once they may have tough or not, arguing about how tough they are

Or

Local teenagers potentially spending the rest of their life on jail for stabbing a farang in the neck and killing him over something so trivial and over being told off for sitting on someone else's bike

OP, son, I'm 73 years old, live here for over 8 years and never hate any people without a really good reason.

The old man you have described must be very unhappy, lonely and bitter.

Leave him to himself.

It does not matter what he says. Nobody deserves to be hurt for whatever they say. Only if they do something to hurt others.

Respect yourself, son. Don't let your hormones, adrenalin or plain short temper do anything you will be ashamed of later.