1. A football stance used to keep their opponent at arms length.
2. A body gesture in which the arm is extended forward with the palm open making the arm erect
,stiff, and therefore immovable, keeping people from entering your comfort zone.
3. A thing people do when they want you to ease on up out their space!
Maaannn...you see dat chicken-head over there, she came all up in my grill so I had to stiff arm her ass. Is that wrong...of course not!