Green’s Dictionary of Slang

1. spec. a section eight discharge, discharge from the US army on grounds of mental instability; also as v.

1944		P. Kendall Dict. Service Sl. n.p.: bucking for a section 8 . . . trying to get discharged for ineptitude.
1952		J. Jones From Here to Eternity (1998) 676: Besides, Jack says they give blue ones with Section 8s sometimes.
1965		L. Bruce How to Talk Dirty 23: A number of guys [...] didn’t report it out of fear they’d be given a section 8 themselves.
1974		(con. 1960s) R. Price Wanderers 97: Lissen, man, are you buckin’ for a section eight?
1990		(con. c.1970) G. Hasford Phantom Blooper 194: I’m not going to be shot. I’m being given an honorable discharge as a Section Eight, a medical discharge they give to crazy people.

2. attrib. use of sense 1.

1979

(con. c.1970) G. Hasford Short Timers (1985) 18: We have already lost seven recruits on Section Eight discharges.

3. a crazy, neurotic or eccentric person.

1960, 1975		Wentworth & Flexner DAS.
1965		D. Pearce Cool Hand Luke (1967) 36: Sounds like you got a screw loose here and there [...] Can’t have no Section Eights runnin’ around in this outfit.
1979		(con. c.1970) G. Hasford Short Timers (1985) 21: Leonard talks to his rifle [...] I don’t think Leonard can hack it anymore. I think Leonard is a Section Eight.
1996		(con. 1946) G. Pelecanos Big Blowdown (1999) 64: The last time I checked, they weren’t handin’ out uniforms to Section Eights.