[Michael Goldsberry]

Bock
German-style beer with a strong alcoholic content. Dopplebock has yet a higher alcoholic content (6% or more) and Eisbock (made with a freezing process) can have an alcoholic content equivalent to wine.

Link

Actually, I think it's German slang for "Drink, you fool!"

[pissant]

From All about beer:

"Bock" does mean "goat" in German and its not surprising that someone drinking this beer would feel a "kick" and make the verbal connection. Once this was done, a strong association formed between bock beer and the goat -- an association that continues even today.