My mom loves to tell the story of the time she was leaving to go to “the beauty shop,” as so many Southern ladies of my mother’s generation call the salon. I don’t know how old I was, but I was apparently well on my way to being quite the charmer.
“Where are you going?” I asked.
“To get beautiful,” she replied.
“Well, that won’t take long,” I said.
My lady and I were laying in bed watching TV.
She started to root through the nightstand for something - when she came upon one of those party pack illuminating sticks that you would join to make “neon” necklaces or bracelets.
She looked at me and said, “So what do you use these for?”
Without even looking, I reply “Midnight ring toss”.
She laughed and open the pack and joined together a couple of small rings.
We both began to twirl these things around our fingers like mini hula-hoops.
She was amused at my lack of dexterity to go more than a couple of rounds before it would fall or fly off. However, she could go on forever.
She remarked, “This should be an Olympic event…”
Tossing the ring back to her I reply with my best sour grapes act…
“Yeah, Special Olympics!”
.
I have a friend who’s very quick witted. A group of us were sitting in a cafe one evening and he laughed at a joke - not so much a laugh as a high pitched giggle.
One guy says “hey man, you laugh like a girl!”
He replies - deadpan, without missing a beat: “Yeah, but I fuck like a hairy biker.”
Ownage.
I was a victim of my own line in this case. My friend was joining my family at a restaurant. He said something to which my joke was, “You are what you eat!” Right after I said it everybody, myself included, noticed the shrimp I was peeling.
This reminds me of the time I was talking to my husband while putting on my pants. I don’t remember what we were discussing, but it was a sober discussion, and I insisted, very seriously, ''Well, I am a very dignified person, aren’t I?"
My husband promptly burst into hysterics. I then looked down and saw that I’d put on my pants inside out, with the pocket flaps hanging down and everything. I don’t think we’ve ever laughed so hard in our lives.
The best comebacks are failed comebacks.
Yesterday morning:
me: ‘‘Are you being a total gigantic nerd by reading X-men messageboards online?’’
Mr. Olives [lifting an eyebrow defiantly]: ‘‘Are you NOT being a total gigantic nerd by NOT reading X-men messageboards… dammit!’’
Friend’s mother to friend seated with me at their breakfast table (middle chool age, after a sleepover):
“Eat your pancakes. Don’t you know there are kids starving in Asia?”
Him: “Name three.”
I still don’t know if it was original or if he picked it up somewhere, but I was mortified and then stricken with giggles. Our circle still uses “Name three.” to indicate the hypocricy of people invoking sympathy for people they know nothing about and do nothing to help, but would guilt-trip you. It’s surprising how often it is apropos.
One night I walked into a store, and there were two teenaged girls in there. I was wearing a polo shirt emblazoned with the old name of the company I worked for. One girl asked about it, and I explained that I work for the company, but they have a new name now. I told them what they name was, and that I wasn’t crazy about it.
One girl said “I like it”, and the other said “Yeah, it’s what I’m going to name my kid.”
When the youngest was a teenager, I asked him to do something and he said he couldn’t, giving the world’s weakest excuse why not. The excuse was so weak that it was an insult to my intellegence that he thought for a moment that I would accept it.
I looked him square in the eye and said, “What kind of fool do you think I am?”
Deadpan, he answered, “Mom, does the kind really matter?”
I cracked up, but didn’t let him off the hook.
I had a friend that used that as a joke way back in the late 80s. I’m not sure if he made it up or got it from someone else.
pantheon, that reminds me of a story my Dad likes to tell.
My grandmother: Eat your supper. Don’t you know that there are starving children in Africa?
My uncle: Mom, starving children in Africa wouldn’t eat this.
Now, interestingly, when I mentioned the story to the uncle in question and an aunt(sister of my dad and the uncle), they both said “I don’t remember that, but it sounds like something your father would have said.” Dad swears that it wasn’t him, though.
Years ago my Dad and I were doing some home improvement when we realized that we needed a studfinder. My Dad went down to the basement to root around for it while I waited not so patiently. Finally he came back upstairs:
“Dad, did you find it?”
“No, it found me”
Badoom-ching. Of course, being 13 or so, I was not so impressed.
That’s fucking classic. 
I was about 13. My older brother was about 16. Somebody flipped him the bird. He shouted at them: “yeah, I’ve got a mother too, but she’s not bald.”
Later I asked him what the hell he meant. He didn’t know. It just came out.
“Fuck you!”
“Get in line!”
When I was in high school, two guys in the marching band were going on and on about something, and it escalated to this point:
“Shutup, Whore!”
“Your mom’s a whore!”
“At least she puts food on the table!”
Friend and I were both class of '89, so middle school would have been mid- to early 80s, but I bet there was a common source. At the moment though, unencumbered by any such suspicions, I thought it was the wittiest damn retort I’d ever heard. 
One that almost got me beat up by a friend we refered to as ‘Man-mountain’.
Him: “Why do you always feel a need to attack my intelligence?”
Me: shrugs “I like a small target?”
Friend walking into our dorm room in college and almost walking face-first into my roommate: “Jesus Christ!”
My roommate, without missing a beat: “How did you recognize me without my sandals?”
Gotta post one of my own here. This was just after the Three Mile Island (nuke power plant) problems in 1980. I am a native of Harrisburg (city nearest TMI) and was at college in North Carolina at the time.
I walked into the room where a friend was just finishing a sentence that ended with “…mutant cows from Harrisburg”.
Immediately I said “Ooooooom!”.
It broke up the room.
Meyer6’s post reminded me of one of mine:
I was walking down 7th Ave one summer day, and noticed a very shapely young Latina who was wearing a tank top, and obviously not wearing a bra. Her nipples must have been poking through her shirt at least a half inch. As she walked past me, she said (in a playful way):
“Why you be lookin’ at my tits?”
I said:
“Hey, they looked at me first!”
…The Aristocrats!!