loco
/ˈloko/ · A1 · adj
crazy, insane, mad, nuts
🚂 Loco like a runaway locomotive: off the rails = crazy
English already borrowed it: going loco means going crazy. Tie the sound to locomotive, a loco that has left the rails, which also covers the rash, risky sense. Un loco is a madman; as slang it can mean tremendous.