Solved about 10 years ago:
"Actually, the answer to this is simpler than that. I learned it from Penn & Teller's book How To Play In Traffic. On pages 76 to 86 they describe a trick you can play on your friends called "I Am The God of Carbonation". They have also done this trick on talk shows. They credit the idea for the trick to Paul Harris (and Eric Mead) in the magic book The Art of Astonishment.
The trick is immaterial to the answer, but it involves agitating one can as much as possible and then claiming you can transfer the carbonation energy from one can to the other. But what it hinges on is this:
I guess they've changed the way they package soda or something. No matter how hard you shake a soda can it takes only about twenty seconds for it to completely calm down....
As long as your God of Carbonation ritual takes twenty seconds or more, the shaken can will not explode. Make sure you hold the can straight up, perpendicular to the ground, and open it all the way with one quick action. That'll get rid of any little bit of fizz that didn't calm down in the twenty seconds.
The answer is that the tapping constitutes a ritual that just eats up time. As long as the can is sitting in an upright position and you wait long enough, the fizzing will die down."