illegally

A new guy came to the club last night. He was playing doubles on the table next to me. I was doing a coaching session, but got distracted by this new player. He was giving a lecture (not in a nice way), to an older female player about how to serve legally. Every time she did it wrong he would...

Sometimes you face an opponent that has an illegal serves. What do you do about it? In my case I tend to say nothing at first, but if he does it again and again I do tell him. Now you know how that is in clubs without a referee.... Some just don't give a **** . What do you do in those cases...