The fool of nature stood with stupid eyes And gaping mouth, that testified surprise.

Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.

There are only two truly infinite things, the universe and stupidity. And I am unsure about the universe.

If you're gonna be stupid you gotta be tough.

Sometimes a man wants to be stupid if it lets him do a thing his cleverness forbids.

Stupidity is also a gift of God, but one mustn't misuse it