A referral to one's self, especially prevalent in the greater London area among young street men. "Mans" is fairly similar to the U.S. usage of the n-word among African-Americans as it is extremely frequently thrown around in the U.K.'s "grime" genre of music, and on the streets.
"I said babe, mans not hot; I tell her, mans not hot." -Big Shaq
"U see, mans is de best footbol playa in east London, ya dun know"