Mine is pretty self-explanatory. Except for the misspelling.
In '94 or '95 my local library got one computer that was able to get on the World Wide Web and one of the apps was a local email (local to Arizona) called AzTEC. Being a major geek i just had to have an email address so i filled out the form and when it came time to enter a password, I got stumped. After several minutes of intense thoughts i came up with sgtpepper, since I am a HUGE Beatles fan, and proceeded to type it in. I tend to type fast, but with a large amount of typos and this was no exception. Before I realized it i had typed sgtpepper as sgtpeper. Now i could've changed it, but one of my most endearing qualities is my laziness, so I never did.
...And that my friends is the story of the handle sgtpeper!