lo·co 1 
(lōkō)
(lōkō)adj.
Slang
Slang
Mentally deranged; crazy.
n. pl. lo·cos
1. See locoweed.
2. See locoism.
tr.v. lo·coed, lo·co·ing, lo·cos
1. To poison with locoweed.
2. Slang To cause to be mentally deranged; craze.
[Spanish, crazy, possibly from Arabic lawqā', foolish, feminine sing. of 'alwaq, from lāqa, to soften; see lwq in the Appendix of Semitic roots.]