Green’s Dictionary of Slang

helium-brain n.

also helium-head
[SE helium + sfx -brain/-head sfx (1)]

(US campus) a silly person.

[US](con. WWII) R. Leckie Marines! 129: I’m gonna teach you helium-heads how to shoot mortars.
Crack the Sky ‘Lighten Up McGraw’ [lyrics] Safety in Numbers [album] Lighten up McGraw / You’re a helium brain / Jog a mile in the rain.
[US]Eble Campus Sl. Fall 3: helium head – synonym for airhead.
[UK]R. Forrest Lark 10: No, this is Oral Roberts, helium head. Who did you think it is?
[US]Spears NTC’s Dict. Amer. Sl. 178: Well, what’s that helium head done now?
V. Lardo McNally’s Folly 90: ‘Fitz,’ I accused, ‘is a helium head.’ ‘But what a dish, eh, Archy?’.