"Knock, knock", "Toilet", says it all really.

Colbert, it turns out, is a fan of the "Bad Kids Jokes" tumblr which does exactly what it says on the tin and publishes terrible jokes that kids think up for, and so he enlisted the help of visiting guest Sarah Silverman in reading out some for all of us to enjoy.

And enjoy you will. And if you need them, there's plenty more where that came from.

Via YouTube