What's the best comeback you've ever given?

Rawr • Swedish. Love red pandas ❤️️
What's the best comeback you've ever given to someone being rude to you or someone nearby? (Or, best comeback you wish you'd given at the time?)
Please describe the situation you were in, and how you dealt with it. 
I wish I had an epic story, but I think the one time it happened to me I was so shocked I didn't know what to say. Lame! I was inspired by an old GoodMythical  Morning (YouTube channel) though, where Link describes what he would want to say: "Sorry, could you repeat that? I want to see if you're stupid enough to say that stupid thing you said one more time."
It's not the smoothest line, but I think I'd feel better for saying it. :D