there is nothing you can do it, exept one thing, but it needs you to be the next school shooter, so no...

Become extremely educated in many things, then argue with them intelligently until they say "Pfft! Your stupid!" (they use improper grammar even when talking), and then counter that by saying that they're the idiot if they can't keep up with an intelligent argument, and explain in very dummy words and tones why you had an intelligent argument, why they were wrong, and why they're an idiot.
It also doesn't hurt to be in advanced classes. Like I'm in a senior-level math class as a sophomore, so when I'm called stupid I can always bring that up.