It depends on what's being drunk . . .

At 125 cal per 12oz, Guiness is about the same as tonic water, and about the same calories as a standard vodka martini. So, if they're ordering 15 or 16 of either, they'd hit 2K calories. If it's some fruity cocktail, like a pina colada, that's over 500 cal per, so they're only 4 drinks away from 2K