The act of going underwater with the exception of your ass and letting out a loud fart. Preferably in the act of an in water dive so as to time it in a manner that you fart as soon as the ass breaches the water. The way a porpoise clears it's blowhole to breathe and reemerge .
When in a pool and you have to fart there is a tough decision to be made. Do you blow bubbles or share with the masses and porpoise poot.
"Dude. Vera will be swimming with the pants porpoise tonight, bro!"
"Dude! Really?"
"Yup. She's finally giving up that poonanny, dude."
"Right on, dude."
porpoise nose. Flipper talking. Needing to back one out so much that air is escaping while trying to hold it in making a clicking noise. Next stage up from a turtle head.