A request to a person(most likely a friend) for sex when you're really in the mood for it. Asking a friend to have sexual intercourse when your body can't hold in the urge anymore.
She called asking me out to lunch but was flirting and acting very erotic. I figured it was a sex request.
A person of the rapey persuasion; somebody who hears "yes please" when everybody else hears "fuck off and don't touch me, you dirty dirty minger". Sex cases can come from all walks of life, but are united by the all consuming urge to sniff your discarded underwear, whilst fapping off to childhood memories of being emotionlessly beaten by their cold and distant father.
Yeah, I wouldn't go out with him, he's a right sex case. You know he's on the register for perving through the nursing home windows and wanking off?
That Josef Fritzl turned out to be a proper sex case, didn't he?