In the so funny it makes me want to cry department:

An article from The Onion: Raving Lunatic Obviously Took Some Advanced Physics.

It's funny, except it's not, because it's probably true, somewhere.
A lot of homeless people are mentally ill, and lot of them are probably perfectly smart and once had bright and promising careers. "There, but for the grace of God, go I" is the sincere sentiment rarely expressed in these kinds of situations--the humility and compassion necessary for that sentiment is usually subsumed in horror and fear. In reaction to that horror and fear we make jokes.

I'm not remotely complaining about The Onion piece; on the contrary I think this kind of dark back-handed humor is what they do best--it will, hopefully, make someone, somwhere think about the reality of the mentally ill when they're done laughing.