Green’s Dictionary of Slang

(US) the van that transports patients to a psychiatric institution.

1976		Barney Miller [ABC-TV] This is [...] [the] 42nd Precinct. Send over a cookie truck, will you? [HDAS].
1984		L. Hindle Dragon Fall 61: Somebody, anybody, get the cookie truck up here, pronto! [HDAS].
2002		icannwatch.com 🌐 You’ve gotta be 100% fruity nutcake in-the-bag, get me a room at the Hotel Silly, hey I’m ready for the cookie truck to come get me type of muthua fu-kin’ crazy to give Afilias one more of anything, letalone a nice plump TLD.