A feeling of incredible satisfaction after taking a swig of Moutain Dew, compareable to various other gasms such as orgasm
Dude 1: "Man!! That was an awesome drink of Dew!! It just tasted so good!!"
Dude 2: "Was it the best drink you've had?"
Dude 1: "Yeah...why?"
Dude 2: "You just had a Dewgasm."