Text Source: Wikipedia
Shotgunning is a means of consuming a canned beverage, especially beer, very quickly by a particular technique involving punching a hole in the side of the can near the bottom.
Punching a hole
To shotgun a beverage, place the can on a flat surface (very important!) and then punch a hole on the side of the beer can. Make sure it’s parallel to the mouthpiece. This is usually done using a key or other sharp instruments.
The drinker then places this hole to his or her lips, tilts the can right-side-up, and pulls the tab in the usual manner. The combined effects of gravity and the pressure change that follow when the tab is pulled cause the beverage to be forced out of the can, and into the drinker’s mouth, very rapidly. Unless one is skilled in this technique, it is easy to become soaked as the drink rushes out of the can.
Warning! Excessive shotgunning would lead to this..