A person being crowd surfed while holding a cardboard shark fin in between their butt cheeks. The privelage is usually extended to someone who did something extraordinary throughout the week.
Although only the one holding the shark fin between their butt cheeks and being crowd surfed is the Party Shark, the entire crowd participating are Party Sharking
1: Congratz on getting your masters degree in Rocket Science, your going to be the Party Shark tonight.
2: Awesome, I'll be over at 10 with my cardboard shark fin decorated with assorted arts and crafts.