1.)A trade of ones food for someone elses food.
2.)Can also be used in a way to mock "scene kids" with there PC4PC or W4W etc.
3.) A very funny insider between friends. (:
Hungry Person2: YEA! I'll totally f4f.
2.)Scene Kid: ZOMGG PC4PC.
Normal Kid: LIKE OMG f4f -____-
3.) "Haha lets make up our own acronym"