Usually said to reiterate the importance of drinking. Just saying "drink" once doesn't convey the sense importance surrounding our drinking culture. Said twice, with some gusto,a party shall evolve, like magic.
Can be compounded by saying "drink" as many times until it sounds something like Drinkdrinkdrkkddir
Person 1 : Yo what do you wanna do today?
Person 2: Drink drink!
Person 3: Yeah man, drinkdrindkdrindk!
When asked if you want a beverage at a social gathering, you ask if they are offering you a drink or a "Drink Drink". A "Drink Drink" contains alcohol.
When Amanda handed me that red cup, I had to ask her if it was a drink or a Drink Drink. Cause I only wanted it if it was a Drink Drink.