Also known as a raspberry, or in some circles, a "zerbert"...a fuzzbutt is the planting of one's lips on a body part of another...and blowing. Creating a "toot" like sound. Often done to babies' stomachs.
When a man or woman finds enjoyment in sticking bottles of carbonated liquid into their anus, and douching their pooper then pushing out the soda so hard it makes their butt fizzy.
Man, that was an awesome fizzbutt, there were bubbles everywhere.