Just throw out comments that you know they will take off on. More often than not, they end up proving their idiocy.
I do this a lot at work too. If I get a racist on the phone...I'm going to mess with them. If the first thing that someone says is, "thank God I got someone that speaks English", I am going to have fun.
Ahaha, some guy I ended up being fairly good friends with said he worked customer support for Verizon I think, and had decent fun. How does a typical conversation go with someone that is happy you speak English? And uhh, it is kind of annoying when I call Microsoft to activate some shit, and get some guy in India, at least he can understand me, lol.