As Chris O'dowd once famously said 'people...what a bunch of bastards'.

Just be overly polite and smile a lot, that will freak them out!!

I know it's rough, but think of it this way: Their life is so meaningless and boring that they have to resort to this. I'd pity them if I were you. Just show them you don't care and their little bit of "fun" will be over soon enough.

Just continue to improve yourself while paying no mind to them. In past breakups that has always been the most positive, effective route for me.

Inform your boss of the situation, just incase they try to cause trouble and get you fired

Work out a ton and get bigger than him, you work at a gym. Then he wont pick on you

They are paying a lot of money just too piss you off. Do they work out our did they join just to piss you off? if it was just to piss you off don't give them the satisfaction, they will get bored soon and stop coming in. But they still get to pay part of your salary for a while.

You should cheerfully introduce her to people at every opportunity. "This is [name], my cheating ex." They can only annoy you if you allow it. Stop letting them do that.

They're just a couple of losers if they resort to that.

Keep going to them gym get strong and beat the shit outta them