Jack just grins, completely at home with the jibe. Being over the top is kind of his trademark, after all. And then he chuckles, and leans over to tease, in a low voice, "Well, maybe next time you should fling your boxers at me! You know, just so we can keep things at the expected level."
He doesn't push about trying to get Ianto up on stage. He does, occasionally, know when to let things go.