Definition of "loco"

Going loco down in Acapulco / If you stay too long / Yes, you'll be going loco down in Acapulco / The magic down there is so strong

1988, Phil Collins (lyrics and music), “Loco in Acapulco”, in Indestructible, performed by Four Tops

Who you trying to get crazy with ése? Don't you know I'm loco?

1993, “Insane in the Brain”, in Black Sunday, performed by Cypress Hill

Holla in New York, fo'sho they'll tell you I'm loco

2003, “In da Club”, in Get Rich or Die Tryin', performed by 50 Cent

You know, I’m a little loco. Kinda crazy, zany guy.

2003 December 15, The New Yorker, page 56

They say that he is locoed. The insane asylums of California contain many shepherds.

1904, Charles Dudley Warner, “The Locoed Novelist”, in The Complete Essays of C. D. Warner‎

A locomotive is, next to a marine engine, the most sensitive thing man ever made; and No.007, besides being sensitive, was new. The red paint was hardly dry on his spotless bumper-bar, his headlight shone like a fireman’s helmet, and his cab might have been a hard-wood-finish parlour. They had run him into the round-house after his trial—he had said good-bye to his best friend in the shops, the overhead travelling-crane—the big world was just outside; and the other locos were taking stock of him.

1898, Rudyard Kipling, “.007”, in The Day's Work‎, New York: Doubleday & McClure Co., page 243