2
general::
1. Drop from exhaustion, faint. For example, After running the marathon, he simply flaked out on the ground. This expression possibly is derived from a now obsolete meaning of flake, "to become flabby or fall in folds." [Slang; c. 1940] 2. Lie down, go to sleep, as in Homeless persons flaked out in doorways. [Slang; early 1940s] 3. Lose one's nerve, as in Please don't flake out now. [Slang; 1950s] 4. Go crazy; also, cause someone to go crazy. For example, She just flaked out and we had to call an ambulance, or This project is flaking us out. The usages in def. 3 and 4 probably are derived from the adjective flaky, meaning ‘‘eccentric." [c. 1970] 5. Die, as in He flaked out last night. [1960s] 6. Surprise, astonish, as in She said she'd just been made a partner, and that flaked me out. This usage appears to be a variant of FREAK OUT. [c. 1970]
American Heritage Idioms