Which side of the can should the hole be made? Directly across from the mouthpiece or the opposite side?

It should be made about 45 degrees from the mouthpiece, as shown in the diagram in the first example. Use the side of your dominant hand for easier opening (for instance if you are right handed, it should be 45 degrees to the right and vice versa). Note, this is a fun party trick but basically it is the same as a double shot of 80 proof liquor from a can that has 12 oz of fluid. Like a beer bong, the sheer volume of liquid that you are taking in can cause a lot of problems such as heartburn, vomiting, damage to the stomach due to the acidity/pH change, and underestimating the amount of alcohol entering your system.