Not novelty songs as such (so no mentions of Weird Al... please) but songs by "serious artists" with lyrics that have made you laugh.

Ones that come to mind:

Pulsallama - The Devil Lies In My Husband's Body
Mountain Goats - Fall Of The Star High School Running Back ("selling acid was a bad idea, selling it to a cop was a worse one")

And I'm pretty sure I did a little laugh at "Fiery Jack" by The Fall. Also "Fell In Love With A Girl" by Brakes ("she was fifty... seven... inches tall").

Now yours!