Not technically a comeback, but it had a similar effect
My old mate had few redeeming features when I knew him but he had a knack for timing... good and bad, appropriate and not...

Best of all was when he got woken up by a knock at the door, and opened the door to a small cluster of Jehovah's Witnesses. Picture the scene, if you will, of 2 sharply dressed men, clutching a bible and wearing a suspicious grin suddenly being confronted with a lardy, bleary, unshaven, greasy-haired Geordie, wearing a Cradle of Filth "Jesus is a Cunt" t-shirt and a pair of boxers with his cock hanging out... and generally looking like he'd been dragged through a hedge backwards.

Apparently the JW's faces dropped and they hustled away with an expression that said "Must... burn... out... my... eyes..." while he collapsed on the doorstep in a state of hysterics.

At least that's the basic story he told me when I went round after work to pick up some stuff. Normally, these kinds of stories are made up, or embellished... but if you ever met the Geordie in question you'll understand why I believe every word of it.
(minister of heresy, Fri 30 Apr 2004, 15:28, Reply)