My dad’s favorite reply to a nosy question was “What, are you writing a book?”
If you made the error of answering, “yes” to that, you’d get the kicker: “Well leave my chapter out and call it a mystery.”
Damn you RoOsh, I was coming in here to say this. I’d originally gotten the idea from the episode of Family Guy where Stewie does this to Olivia after she used a dated Weakest Link reference. I’ve only used it a few times, but I don’t think there’s an effective defense for it. If they play along, they are either too stupid to realize you’re insulting them, or conceding that their comment was dumb. If they try to throw more at you, it just provides more ammunition. And if they shut up, well, that’s what you wanted anyway, isn’t it?
Yeah? Well, your mama’s boots have instructions written on the heel.
(When he’s been poor-mouthing a friend of yours,) “Really? She’s always spoken well of you.”
(With raised eyebrows,) “What a peculiar thing to say!” Say it very coolly, no matter how angry you might be.
Once in a great while, a guy will be so boorish as to insult the internal muscle tone of a girl he dated. “Like stickin’ it out in the yard!” The proper answer; “If you’re big enough, it’s all tight.”
I always like this one when my kids are not putting on their best behavior in public, and some know-it-all thinks they know better than I do how to manage them:
“Thank you for the unsolicited advice. Next time I need some, I know who not to solicit it from.”
This is a very effective strategy. I just want to add that you can give it a very sweet extra twist if you want to, or if the occasion warrants it.
What you do is you analyse and deconstruct the joke at tedious length (as per RoOsh’s excellent example), but you deliberately get the analysis wrong. It might sound something like, “Oh that’s very witty, I see what you did there. You built up to the end and then used ‘mother’ which sounds like ‘other’ and you’re suggesting you slept with someone other than who we thought, which is a very clever joke, well done.” (Not a great example, but it will do for now.)
At this point, the other person can either back down, defeated, or - and here’s the good part - they can start trying to explain the joke properly. This is the sticky trap from which there is no escape. As everyone knows, someone trying to explain how a joke is supposed to work or why it’s meant to be funny can never look cool or win. It’s impossible. As soon as they take the bait, they’re toast. It’s a wonderful tar baby.
You won’t realise how evil this is until the day you try it and it works.
When someone asks me a question that is overly personal, I tell them that if we were close enough for me to share the info, they would know all about it already.
Eddo Brandes, but yes. I like the one about Hughes threatening to bowl someone a piano “and see if you can play that”. 
Michael Atherton was once called a “fucking cheat” in Australia after refusing to walk when the fielding side thought he’d got a faint edge and been caught. He merely said serenely “When in Rome, dear boy”.
I really and truly and honestly believe that completely ignoring someone is the best tack, especially if the asshole said whatever in front of others. It makes THEM look stupid to be ignored.
My second choice is to punch the person in the mouth. Hard.
This would work awesome if you/I could deliver it in Alan Rickman’s voice.
If the recipient of the comeback is female, wait until she has turned to walk away, then say to the others around you, just loud enough for her to hear, “That was a dude.”
Stolen from Triumph the Insult Comedy Dog, a gold mine of comebacks.
I have an acquaintance who always tells other women that they look tired. This is said in a faux-concerned voice, as if she’s just so worried about her dear friends, but is meant as a nasty insult, as in “You look like shit.” It’s totally underhanded. I planned for the next time she did it to me, and I was prepared:
K. Oh Sigmagirl, you look tired!
S. Thanks! So do you!
K. 
The trick was to answer her without hesitation, and as if she’d paid me the most lavish compliment I’d ever received. She couldn’t possibly dismiss it, because she’d just done it to me, and if she acknowledged it was an insult, she’d incriminate herself.
Worked like a charm.
hehe. Yes, when I’ve said this (maybe 4 different times) I really mean it, and that sorta voice comes naturally.
I’m with you on this one.
Or you could say “WHO THE HELL WAS THAT GUY?”
This thread reminds me of an incident that happened years ago when I was in my teens.
We were at McDonalds and they were offering Star Wars collector cups at the time, my friend placed his order…Big Mac, large fries and a large Coke… and the girl behind the counter said “Would you like a glass with that?” he said…“No, just pour it on the fucking tray and I’ll lick it up!”. The look on her face was priceless, and needless to say we laughed like fools the whole day.
Not to brag, but when my brother and I get into verbal fights, I usually beat him by a mile.
Unfortunately, I can’t think of any specifics right now. You’re just going to have to trust me.