Green’s Dictionary of Slang

crazy, mad, whether because of taking drugs or one’s emotional state.

1985		T.R. Houser Central Sl. 69: loc Loco.
1994		G. Smitherman Black Talk.
1995		L. Stavsky et al. A2Z 64: crazy – She’ll go loc if you leave her now.
1999		Eble Campus Sl. Nov.
2000		Hip-Hop Connection Jan.–Feb. 54: Loc. Multiple meanings for this one. Firstly it’s an abbreviation of ‘loco’, which is Spanish for mad.