Dabbing on a nigga is basically the modern day dance move but only doing the dance repeatedly and saying "Dab on a nigga!" over and over. It can be done after you win an argument a roast or just saying dab on a nigga for no particular reason, it can be done in any sort of context.
A person who is lame; in actions, speech, or overall demeanor. One who is lame.
"Man, why you playin that gig from Jon B?"
"Yous a ol' popcorn ass nigga!"
"Why you listen to that popcorn music?"
"Man, stop lettin that bitch hit on you like that, ol' popcorn ass nigga?"
"You a popcorn ass mutha fucka!"