2. Hot chick who never seems to go out with anyone.
3. A female that you know you can't become involved with past the point of friendship. This may be due to having a boyfriend/not being interested in you/or too busy to be involved with anyone. She's like the real forbidden fruit. You can't have a taste of her.
You know that really hot chick who won't seem to date anyone? She's forbidden fruit.
You know that chick who's quite prude? Her snatch is the forbidden fruit.