AF means "As F#ck". For example: "UR cool AF!" meaning "You're cool as F#ck!"
See AF T-Shirts at amazon for lots more ways to use the acronym AF.
What does AGG mean in text?
What does DYK mean?
What is the slang definition of Bah?
What does NATM mean?
What does FBF mean?
What does Player stand for in internet slang?
What does OYO stand for?
What is AMC short for?