Here's how 'slappin' the bag' works: Obtain boxed wine. Open the box. Take out the bag of wine. Have a friend hold the bag up for you at face-level wherever that may be. Put your lips up on the spicket and open the valve. Suck/chug the nectar until you've had a respectable portion. Close the valve. Take your face off the spicket and give that naughty bag a slap like you mean it. Then take and hold the bag for the next person. GET BLASTED.

A drinking game in which you slap a cheap bag of wine (conveniently found inside a box of wine) and than take a big gulp from it. Known to create treasured memories you don't remember and pounding hangovers.

Awkwardly chugging beer out of an indian sachel in Applebee's the restaurant, while simultaneously slapping it like a naughty baby's bottom.