When someone acts like butter couldn't melt, but secretly they're a total bitch
Person 1: Hey did you see Madonna fall?
person 2: Yeah, but she's such an undercover-bitch, it was totally karma
Similar to frenemies, but more devious & calculating. People who present themselves a particular way publicly, but are really screwing with others behind the scenes. Sometimes they even attempt to be life ruiners. If you do not know what is going on behind the scenes, you would never realize they mean you no good.
I met this incredible man, and was talking to a couple of friends about how special he was to me. Next thing I know, he is suddenly acting like I hurt him. I found out my "friends" were lying to him about what I actually said. What a couple of undercover bitches.