Excellent.

I and a couple of colleagues met a guy the other day who made a racist joke. We just looked at him as if we didn't get it and he started digging himself in deeper and deeper. We kept looking at him. Then he said, "Have I said something that's not very PC?" (As if he didn't know!). "Little bit", we said and then he started apologizing. We didn't plan to do this, it just kind of happened, but he ended up pretty embarrassed and hopefully will think twice in future.