A "Mouf Piece" is not a grill, or lawyer. It is the way you can spit yo game to the females. If one does not posses this ability, then he who shall not aquire a mouf piece, shall not get laid.
Nerd: Hey, Want to go to the dance next week?
Sexy female: *Ugh* No, geek!
Mouf Piece Person: Say Lil' Momma, wanna ditch the party and head to my crib, and kick it?
Sexy Female: Helllll yeah! *pulls out a Magnum condom*
A test to determine the paternity of a child/baby daddy. Typically, the process involves the use of a cotton swab on the inner cheek to extract DNA of a black man or other minority.
"Dat bitch went to court and now I gotta get my mouf swabbed but I know fo' sho'some other nigga da one dat got dat bitch pregnant!"