when a male or female is fingering his or her woman:
he/she places 4 fingers inside the girl with a flat hand resembling a sharks fin. then making wave like motions with the hand when all of the hand other than the thumb is inserted.
shark finned fuck out that bitch last night!
i was hefty sharkfinning at the weekend
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).