Undercover Freak 

Someone who appears to be innocent when it comes to sex, but what lies under this person's innocent appearance is a sexual freak. Could apply to "tame" looking people who are sexually wild, or a person who is into sexual kinks. Can apply to women and men, but used often to refer to women.

I brought this one girl home. I was afraid of what to do because she seemed really uninterested in being more than friends, but when I walked in on her completely naked in my room, I realised I had brought home an undercover freak.

Undercover Freak by RandomBro November 6, 2013

Undercover Freak 

The girl who claims that she is not sexually active, and never has been, but at a closer look has a different guy over every weekend to "watch a movie." She will claim that they just "snuggle," but it becomes harder to believe with each stranger she brings home.
It is possible she is a compulsive liar, or it is possible that she just has paternal "daddy" issues.

Guy A: "Yo, that girl Haley isn't down for anything."
Guy B: "Nah, bro, word on the street is she's an Undercover Freak, and she's good. She just keeps it on the down low."

Undercover Freak by r00m13_rev October 12, 2012

Undercover freak 

The girl that appears to be perfect to all adults, but she is really a cock slut.

I got a girl who is an undercover freak so mother doesn't care if I stay out late with her.

Undercover freak by Stan, Cody, Ricky, and Alex April 2, 2003

Hello kitty undercover freak 

A girl 17 or older who really likes hello kitty and seems cute and innocent, but turns out to be really freaky in bed. (in all good ways of course.)

Bro talk: man, I met this girl who really likes hello kitty man, and I thought she was gonna be pretty regular in bed but dude, I'm telling you. Total freak, and I love it. She's a hello kitty undercover freak!

Hello kitty undercover freak by George hernandez September 14, 2012