A pretty girl who through some mixture of cluelessness, being otnay ootay ightbray, naivete, or low self-esteem, really believes that it's a terrible thing for a guy to get aroused and not cum, and therefore can easily be pressured into doing something about it. Most guys won't clue them in for obvious reasons, and they tend to have few girlfriends to tell them because other girls won't hang out with someone that slutty. When some kind person finally does tell them, they're usually angry for a couple years!
Monique the Slut in the early years of SinFest was pretty much just a cum bunny.
Guy: Can I kiss you goodnight?
CB: Oh, sure.
Guy (after groping her during the kiss): Oh, god, that was so hot.
CB: Uh, yeah, I have to be at work early --
Guy: You can't leave me like this, not after that hot kiss you gave me and letting me touch you that way!
CB: Oh, well, look, can I just give you a hand job? I'll take my top off.
(Two minutes after he leaves ... guy on cell phone to friend): Dude, you weren't kidding! She tried to get rid of me with a hand job and I told her she was killing me so she sucked.
Cum Bunny (sobbing alone in room): I don't know what's wrong with me! I get guys all turned on all the time! Why can't I control myself!?