Green’s Dictionary of Slang

ha-ha n.2

[abbr. brewha n.]

(US campus) beer.

[US]Eble Campus Sl. Mar. 4: ha-ha – beer: Let’s go for ha-ha’s and za.
[US]Eble Sl. and Sociability 63: A ‘beer’ is called [...] a ha-ha because of the pleasure of drinking it.