I was looking for a new username for something and couldn't think of anything. I love the band The Mountain Goats, so with lameness set to overdrive, I typed in iamnotthemountaingoats. I didn't intend to use it for much, but realised I really hated my old usernames. As it was way too long, I shortened it to 'imnotgoats', which I preferred immensely, and started using it.
It was inconspicuous enough that no one would ever know where it came from, unless there was some kind of 'what's the story behind your username' thread on a web community, which is, of course, highly unlikely.