How can you feel 'prep', isn't that like when you act all... idk, I've only ever heard in reference to American stereotypes, and I don't hear them too often. And it was a fashion thing with polo shirts and stuff...
Very superficial, characterized by the excessive screaming and repeating phrases such as "oh my God" and "like" over and over again, looks down on anyone who isn't wearing exactly what they're wearing, also looks down on people who ARE wearing exactly what they're wearing, because they MUST be copying them, and besides, they can totally pull it off better anyways, in their mind. Get up two hours early to do their makeup and hair. Flirt with anything that moves, but act all disgusted when one of the objects of their affection asks them out. Generally think way too highly of themselves. Not usually very smart.