A person who has many friends from many groups and circles, who always tries to please them all at the same time and desperately tries to keep them all seperate because they insist, which inevitably and consistently results in some disaster that said person is sure to be blamed for, yet has nothing to do with anything.
Monica: Pheobe is at the coffee shop with Joey and Chandler, regardless of their feud with Ross. I mean, doesn't she have any loyalty to my brother!
Rachel: Pheobe is such a Friend Whore. I'm not listening to her Smelly Cat song anymore!