The title says it all. Post what the worst message you've ever gotten on your computer. I have several:
copvampire has logged on.
Green BH has logged on.
Greatnes67 connected.
OS Paged Pool memory has run out. Source engine will now crash and burn.
Runtime has encountered an error and has forced this application to close in an unusual way.
Your ATI Graphics card cannot connect to the power supply properly. Please check the connection or refer to the manual.
Also, if you have more than one, post them in one post. If you come up with another one, modify the old message.