From the episode "Laundry" from Jake and Amir. When two guys hang out and start crying. Amir does this often around Jake for no apparent reason.
Amir - Look at us crying up here like a bunch of ninnies. Heh, everybody turn back, don't look at us. Two dudes, two grown men, just sharing a beef.
Jake - What's a beef?
Amir - We're beefing right now!
Jake - No we're not.
By Elisabetta
Beefing
An intransitive verb describing the state of being in which one is disagreeing with another; usually associated with blacks.
Black person 1: "Ay, that nigga be beefing wit' Young insert noun/proper noun."
Black person 2: "I kno'. Dey be fightin' ova shit all the time."