Gabriel just might be misunderstanding one or two of the fundamental aspects of a bachelor party, here. Were his mind on the matter, Peter would probably have misgivings about letting Gabe organize a party for him, but he's barely following the current conversation.

Shit. Shit, has he been staring? Question, question, probably only going to get to ask one question --

"What are you?" he blurts, completely failing to be in any way casual about it.