I need your help!

I need a good joke to share for Tuesday, but I'm drawing a blank and all these joke sites make me want to murder the person whoever thought pop-ups and MS Comic Sans were cool.

So the question is...what's your favorite joke? One that isn't too dirty or offensive (it's for class).

I'd use my favorite joke, but it's kind of offensive (or at least, insensitive) to the French. :\