If you liked Al Jaffee's Snappy Answers to Stupid Questions from MAD Magazine (and if you didn't, boy are you in the wrong place!), I think you'll enjoy this Reddit thread: "What was your best "comeback line" that left the other person totally speechless?" There's plenty of stuff that I'm betting is really esprit d'escalier, but if even half of it is genuine, it is proof of some fundamental rightness woven into the very fabric of the universe.
What was your best "comeback line" that left the other person totally speechless? (self.AskReddit)
davidtregaskis: While working at a paint store my assistant manager was giving me grief because I wanted to get off early to go take a final. She said, "when I was going to school and working if there was ever a conflict between school and work, work always came first." I replied, "that's probably why you're still working here."
Texanjumper: "Brother (our parent's biological child) was talking about how he was the favorite child. my response: 'Well they picked me, got stuck with you!' he had nothing left to say."
gschoppe: "LOL... my adopted sister used that on me once. Being the big brother, and thus obligated to have an immediate comeback, I said, 'Yeah, but have you seen the other choices they've made with their lives?' She never used that line again."