Green’s Dictionary of Slang

(US gang) like a mother fucker; when added to a gang name it implies the toughness and aggressiveness of the person so defined.

1966		H.L. Foster ‘Cant of the Disadvantaged, Socially Maladjusted, Secondary School Child’ in Urban Education Jan. 108: l.a.m.f.: like a mother f———.
1970		G. Cain Blueschild Baby 68: A court of his acknowledged peers will try him. [...] We are his brothers. Not that blind bitch downtown holding scales. Guilty, guilty, L.A.M.F. is the verdict of the people.
2002		J. Nikolai ‘More Lame than L.A.M.F.: The 17th Annual Rock And Roll Hall of Fame Induction Dinner’ in Punk Mag. 🌐.