Green’s Dictionary of Slang

fumigate (one’s brains) v.

(US campus) to smoke.

1881		A.A. Hayes New Colorado 121: ‘Stranger, do you fumigate?’ ‘If you mean smoke, sir, I do not.’ [HDAS].
1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 38: fume, v. [...] fumigate, v. To smoke.
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad 64: Fumigate your brains Smoke a cigarette.