Oh, man, this comeback insult is a bit over-the-top, so if you offend easily you can move on.
When I was going through Navy basic training in 1998, a particularly homophobic fellow recruit (a ways back into the don't ask don't tell days) said to our division commander (same as drill instructor) a typical crusty Navy Chief Petty Officer, in front of the whole division, "what do I do if I know my rackmate (bunkmate) is gay and I want to be assigned to a different rack?"
Well, I guess it's his fault for setting himself up like that in front of everyone, but our chief, without a moment of hesititation, replied:
"How do you know he's gay? Does his dick taste like s**t?"
Very off-color, I know. Sorry.
That is just priceless, Flick! I laughed so had, I nearly snorted coffee out of my nose!