There's nothing at all wrong with some friendly smack talk, but I don't think you jump right in if you're the server. Maybe start off by asking how the customer's night is going, have they been in before?, etc. Establish the fact that you're polite and friendly. Maybe a little later, you slip in a crack about the shirt, along with a smile. Now you're just being playful, instead of acting like a jerk.

It's not that hard.