Green’s Dictionary of Slang

1. (US, also hamburgerhead) a stupid or worthless individual or creature, i.e. one who has no more brains than a hamburger.

1933		W.R. Burnett Dark Hazard (1934) 89: Them dogs you saw were all hamburgers. Wait till you see the real dogs run.
1955		R. Bissell High Water 94: He had been pulling all this stuff for years and getting away with it, which just shows what a grand and glorious country of opportunity for hamburgerheads we got.
1961		J. Brosnan Pennant Race 8: One loudmouth cried, ‘Go write a book, you hamburger!’ [HDAS].
1975		J. Wambaugh Choirboys (1976) 286: This hamburger they were busting thinks he’s Kung Fu.
1988		C. Robbins Ravens (1989) 306: ‘Hamburger’ was the vogue word among the Ravens at the time to denote a swaggering, boastful John Wayne type.
1993		Watson & Dockery Point Man 53: Why don’t you hamburgers try and set some sort of record for your class [HDAS].

2. (drugs) MDMA [? the circular shape of the tablet].

1996

Alasdair Forsyth ‘Ecstasy and Illegal Drug Design’ on DrugText.org 🌐 Ecstasy brand names: SHAPE [...] (disco) biscuit [...] white biscuit [...] mini snowball pellet [...] brown biscuit [...] (disco/ham)burger [...] grey biscuit.

3. (N.Z. prison, also works burger, the) constr. with the, a life sentence.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 83/2: hamburger, the (also works burger, the) n. a life sentence.