I got my first computer user account of any kind my freshman year of college. I was sitting trying to think of something witty that was biology-related, since I was a biochemistry major, but they were all taken! Finally, I looked up the first reasonable word in the glossary of a textbook... voila. I've been acrosome ever since. (An acrosome is the enzyme packet on the tip of a spermatozoon that is used to eat it's way through the outer wall of an egg to fertilize it.)
The BEST biology name I've ever seen, though, was a guy who called himself NaKATPase...