the movie Tommy Boy is one of my all time favorite movies and my name is Tom, and my nickname in highschool was Tommy G so it just kinda evolved from that.
Other ones I've used
Jolly Roger - if you are a Jimmy Buffett fan you'll know this one (jolly roger flag), or a hockey fan (it's a painful hockey move)
tgardone - Tom Gardone.....do the math
da_man9769 - I'm da_man......my car is a 97 and I like the number 69...(who doesn't???)