Why I drink is a phrase derived from the animationRamshackle by Zeddyzi, specifically a common line for the character Stone. The phrase why I drink or This is why I drink can be used to denote extreme agitation or annoyance.
A line that would not nearly be as memorable if it weren't for its pitch-perfect delivery.
"As a sports metaphor? (“Let’s face it. The Celtics drank the Knicks’ milkshake last night.”) An amorphously obscene double entendre, hearkening back to its Kelis-ian roots? (“I’d like to drink your milkshake!”) Or maybe, in a nod to the godlike venom of its utterer, a taunt: “You best back down before I drink your milkshake, bitch.”
--nymag.com