Fat and Friendless. An acronym used to describe people who are both obese and unsociable. Can also be used sarcastically or as an excuse.
"Pfft, I dont have a date to prom, im too FAF"
"Hey look at that FAF'er over there without a date"
"Why would I be friends with him? He's FAF..."
Jenny: Why aren't you going to the party tonight?
Nick: I'm FAF.... duhhhhh!