to "hoist by one's own petard" means you have been hurt or caught by the very device that you intended to hurt someone else. This phrase is often used mockingly, as if to say that you stepped in your own mess.

Petard is nothing to do with retard. You are retarded, not petarded. :P

bruh you a petard?

peter stop being a petard and quit lighting my hair on fire!

That kid with the big head is such a petard.

You know those dicks drawn in sharpie in the public bathroom? Well thats just another petard.

"Did you see that guy giving me those ridiculous pick-up lines?"

"Yeah, he was petarded!"