A mutha fugga/ mutha fugger is slang term for mother fucker or relating words. Ex. Fugged up= fucked up.
Kid in school: I beat that mutha fugga up!
Teacher: Go to the office!
Kid in school: I said mutha f u g g a.
Teacher: Take your seat MuthaFugga!
Anal sex that is messy and stains things.
Skeeter did stainal with his sister on my couch now it's ruined!