How can I remove some carbonation from soda?

Take the soda in either can or bottle, let it sit in the back seat of the car during hot day. 
Gently remove cap,  Place your thumb over opening , shake it for all your are
worth and then.....
aim it at someone you really want to get even with and move your thumb........

Squeal really loud, start apologizing profusely and then run.

Then go get a Crystal Lite (add rum if desired) and remember the expression on their face,.

Mwaaahhaaaahaaaa.  

Sounds like even more fun!