Green’s Dictionary of Slang

(US black) to go crazy.

1995		L. Stavsky et al. A2Z 64/1: locin’, locin’ up – v. going loco or crazy, especially when gang members are preparing to fight.
2000		Ebonics Primer at www.dolemite.com 🌐 loc-up Definition: to go crazy, get in a fight. Example: Yo, those niggas betta stop steppin befo I loc-up o dare asses.