Fake Girls are the obnoxious suburbanite females between the ages of 14 and 19 that act as though they were being filmed for an MTV reality show. Most of what they say sounds as though it was written or scripted out, even though they don't think before they talk. They also appear to put out sexually, but don't deliver. Usually they end up dry humping and calling it a night.
By college this usually wears off, and Fake Girls fall into a trend that is basically free prostitution. At this stage in the game, they're putting out...to everyone they see.
On rare occasions these traits carry into adulthood, and can be seen in some women that reside in the upper middle class of society.
Luke: Hey I heard you went over to the Julie's last night, what happened!?
Vern: She sloppily made out with me, rubbed her thigh next to my nads, and two minutes later said she was to tired to carry on.
Luke: Hasn't she done this to you like five times?
Vern: Yeah...what a Fake Girl