Ok, I sent this question to Cecil, and got an “automated” reply from Jill advising me to put it to the “teem” here first…so, here goes.
I’m 35. My daughter is 13. The other day she showed me that if she put her finger into the fizz of a freshly poured cup of soda, that the soda will “fizz down” (dissipate) faster.
Silly me, waiting for my sodas to “fizz down” at the natural rate my whole life, and she figures out a better way at age 13.
Of course, her first question: why? Hmmm.
Hmmm indeed. My first thought was that perhaps it is the salt from the human skin chemically interacting with the “fizz” bubbles, and somehow creating this “fizz shockwave”.
So, I poured a new cup of soda (into a new cup), and added some table salt to the fizz. No joy. No reaction whatsoever.
Then, I figured that perhaps it is the heat from the finger that sparks the “shockwave” (you know, heat makes the bubbles expand, blah blah)…
So, I heated up the fat end of a butter knife and stuck it into yet another freshly poured cup of soda fizz. No joy.
Having my mental sleeves now rolled up, I conducted the following “experiments”, which ultimately gained zero ground as far as an explanation goes, but perhaps did serve to identify at least some of the variables of the equation. Here’s what I found…
The “fizz” dissipates faster WITH a finger poked in it:
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Regardless of whether it’s poured FROM a 2 liter bottle or a 12 oz. can.
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Regardless of whether it’s poured INTO a cup of plastic or of glass.
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Regardless of whether it’s “regular” or “diet” soda (although I think it’s more aggresive in diet).
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Regardless of whether or not ice cubes are present in the cup prior to pouring.
One interesting thing that I have noticed, however…if I pour a cup of soda into cup “A”, and then “finger” it (to speed up the de-fizz), any subsequent pours of soda back into cup “A” de-fizz at the ACCELERATED rate…regardless of whether I “re-finger” it or not! ??
Ok, “teem”, what’s the scoop? 
JJ Richard