Re: mentos and coke.
Wow! The vids I saw was people just sliding the mentos (quickly) into the bottle which is sitting on a surface then getting out of the way as it sprays upward. One of the clips on youtube is some sort of TV talk show, and they say that they're only using diet Coke because it's less sticky than regular coke.
As for how to launch the bottles, early on in the Carlos posted, if you listen closely at the beginning it sounds like one of the cohorts asks if the lid is loose enough. So, I would guess you dump the Mentos in, seal it up, but not too tight, then bounce it off the pavement. Let us know how wet you get.
Ever wonder who comes up with this stuff? It's all over youtube. Someone must've said, hey let's put some Mentos in Coke and see what happens...