Although some people may think so, a "prep" is not always a negative thing. A prep is simply someone who wears clothes that are in-style (Hollister, American Eagle,...etc). Preps usually:
-say "like" a lot
-wear expensive clothes
-have a purse
-are still in school (including college)
-are friends with mainly other preps
-are part of a clique
-straighten their hair
-do their nails
-end up getting a nose-job
-wear bows in their hair
this isn't always negative, though. Preps and emos tend to be opposites, but that doesn't always mean they hate each other.
prep1: omg can you believe Shannon broke up with Tyler?!
prep2: no way! I saw them making out like yesterday!
prep1: omg i know.
prep2: omg i can ask him to the dance tomorrow!
prep1: omg you're such a slut, lol
prep2: omg i know, lol