It's called that because it sounds like ass. This is my first song that I actually recorded and put on the Internet. A few days ago both the tune and most of the lyrics somehow came into my head, and I thought it would be fun to actually release it. It ended up sounding somewhat different than I imagined it, but I just can't be bothered to spend any more time on this joke song.

Lyrics:
There's a new girl in town, her name is Twilight Sparkle.
She's a librarian, maybe you heard about her?
Whenever she goes by, it's like a rip in spacetime,
Like gravitational field's pulling towards her backside.
She never skipped a class, she never skipped a lecture,
Just like the royal ass she studied to perfection (she studied to perfection)
Oh, Twilight's got the biggest ass in town,
She never skipped a class
Of Sunbutt 101.