Sarcasm
Depending on how it's used, sarcasm can be a defense against stupidity or stupidity itself.

Stupidity: When someone asks someone else a decent question and they reply rudely with unneeded sarcasm.
Defense against stupidity: When someone asks a stupid question that more than deserves a sarcastic answer.
When I asked Jo if she was gonna order ramen again, she said "Nooooo. I'm not gonna order what I order every day."
That sarcasm was totally unnecessary, and stupid.