Pretty Fat Friend~ the friend of the hot chick that every man has to deal with to get to the girl they want.
Or the not quite hot chick that all super skinny 'I'm fat' girls hang out with to boost their self-esteem.
Seedefinition=You know you know a girl who has at least one pff around her at all times.
Pff is used to say something like "pff" or pfft". But it's also used in a fandom called "My Little Pony" and in that fandom "Pff" means "Pony Friend Forever" you can also say it like "bpff" Which means "Best Pony Friend Forever"