Flippy Shit is a slang term given to wrestling moves that are little more than bellyflopping or sitting on your opponent, but with a bunch of unnecessary flips and twists to make the move more exciting to watch -- and more dangerous to perform.
The IWC loves these moves, as they have completely confused wrestling and gymnastics. As a result, many vanilla midgets who can't actually have a decent match have picked up doing these moves, and confuse people into thinking they're good wrestlers.
That's not to say all wrestlers who do Flippy Shit are bad. Shawn Michaels, Chris Jericho, and Rey Mysterio are all phenomenal wrestlers who have figured out how to incorporate Flippy Shit into a decent match. John Morrison got pretty decent at this, too. Evan Bourne is terrible at it.
X-Pac did flippy shit all the time in his early career, but had to tone it down after a series of neck injuries, and became a better worker for it. Japanese wrestler Hayabusa once missed a springboard moonsault, and paralyzed himself for life.
Flippy shit doesn't take away from one's athletic ability, but can be a huge "cheat" in getting over with the crowd, and can cheat one out of a long-standing career.