Anecdotal evidence has it that a bottle of soda that was heavily shaken will not bubble over if tapped at the side multiple times.
Yet I wonder: Has the tapping really any effect? Or could it be that the mere time that passes while tapping at the side of the bottle has the carbon dioxide not mixed with the soda anymore?
Well here's an unexpected source: Steve Spangler Science!
Apparently after shaking, there are bubbles left on the sides of the can (or bottle), under the liquid. Since the soda is supersaturated with $CO_{2}$ the bubbles become nucleation sites for the conversion of aqueous $CO_{2}$ to gaseous $CO_{2}$. Since there are many bubbles, and since they're under the liquid level, there is a quick increase in the volume of gas inside the can, and the liquid is pushed outwards as the gas tries to escape the liquid. Evidently tapping the can before opening it dislodges the bubbles under the liquid, decreasing the amount of nucleation sites below the liquid level. Therefore when opening the can, there is no sudden overwhelming conversion of aqueous $CO_{2}$ to the gaseous form inside the liquid, and the liquid does not gush out.
Of course, if one waits long enough after shaking a can, the bubbles stuck on the side will eventually rise to the surface, and the can becomes safe to open again all by itself. This does require some time though, more than the few seconds that someone would spend flicking their can.
