Just for funsies, I slipped this snippet into my former company's error handler CGI. (a simple CGI that caught ErrorDocument redirects from Apache, then printed an appropriate HTML message based on the code).
On top of the 'real' message, I put in the output of this snippet. I ran it 30 or 40 times, funny, not too risque for my boss. No problemo.
2 months later, I am called by the secretary asking why our web site is saying that she has sex with the boss's 8 year old son. There, in living HTML was a BOFH message on her screen.

JUST IN CASE you were thinking about putting this in a 'real' place. Don't :)
-oakbox