Green’s Dictionary of Slang

loc adj.

also lok
[loco/loca adj.]
(US black)

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

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