can't fix stupid
The case of being confronted with a problem that is utterly someone else's fault, in which case can not be fixed by yourself, the person that caused it or anybody else.
I can't fix stupid.
you can't fix stupid
The response to seeing some moron doing something incredibly asinine.
Eric has a poisonous pet albino monocled cobra as pet. It bit him and almost killed him.
You can't fix stupid.
You can't fix stupid.