Some one who fucks your mother. Also a word known for coming out of Rappers mouth's such as Lil Wayne, and T-Pain.
"Fuck land, I'm on a boat, motha' fucka (motherfucker)
Fuck trees, I climb buoys, motherfucker (motherfucker)
I'm on the deck with my boys, motherfucker (yeah)
This boat engine make noise, motherfucker" (On a Boat Lyrics)
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.