1) The muffin chopper is an anus or ass; the part of the human anatomy used to "cut a muffin". The "muffin" is a light fluffy fart or poot.
2) A female's ass which is particularly attractive.
Brak: OMG, look at that muffin chopper in the crosswalk!
Zorak: Mmm, I'd like to wear that for a hat!