A guy was wondering what being a suicide bomber was like...

A guy was wondering what being a suicide bomber was like
So I told him, "C4 yourself"

This is a pun. The pun is centered around the word C4, which is pronounced exactly like "see for", so the listener wouldn't be sure if the jokester were encouraging the guy to blow himself up with C4, or if the guy was encouraging him to become a suicide bomber. This is perhaps more funny than most puns, because both meanings are pretty darn similar - it almost doesn't matter which meaning the person  understood the person to have been saying, since both are so similar.