When someone invades your personal space or privacy with the effect of causing harm or distraction. A person maybeef the grill of another without necessarily intending to.
"Yo, why the fuck you all up in my face, beefing my grill and shit?"
"Man, Mitch just wouldn't leave me alone about that cigarette I 'owe' him. He was totally beefing my grill."
"Tyrone was beefing my grill hard, so I clocked his ugly face in."
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.