fruit loop, n.² — Green’s Dictionary of Slang

fruit loop n.²

[pun on the US breakfast cereal Fruit Loops/loopy adj. (1)]

(US) a crazy or stupid person.

1987		Athens (GA) Banner-Herald/Daily News 8 Aug. 8: It’s sort of a national Fruit Loops day. Lots of windchimes.
1991		P. Cornwell Body of Evidence (1992) 49: You got any idea how many frootloops call in this kind of crap on a regular basis?
2005		L. Fugett Butcher Holler 57: My staying doesn’t appear to be a matter of choice, not according to that skinny fruit-loop you bribed this morning.
2007		L. Redhead Cherry Pie [ebook] For all I knew she was a total fucking fruit loop.