A slutty person that comes into a new social scene (different school, group of friends, etc.) and burns very brightly. After a solid period of fucking anything with a rounded edge, they completely disappear; leaving suddenly to whore-around somewhere else or abruptly stopping they're skeezy behaviors (burning out-- never to slut again.)
A: Everyone in this house has slept with Alex.
B: Alex, who?
A: Oh, shit. I forgot he transferred like a week ago.
B: Just a slut comet moving to another galaxy
A: Maybe he'll orbit back in like 300 years?