Chuck Norris and Superman fought each other on a bet. The loser had to wear his underwear over his pants. (Submitted at the request of my 10 year-old son.)

Superman wears Chuck Norris underpants.

Some people wear Superman pajamas. Superman wears Chuck Norris pajamas.

Kryptonite has been found to contain trace elements of Chuck Norris roundhouse kicks to the face. This is why it is so deadly to Superman.