A shitflip is to attempt to kickflip or heelflip or any other flip but have the board completely fly away from you when you kick thus causing embarrassment and making you look like a total dork.
We've all done shit flips. :D
Skater 1: "Duuuuuude check out this sweet quad kickflip."
Skater 2: 'Yeah right, lets see it."
Skater 1: -board flies 20 feet away, gets run over by a car-
Skater 3: "wow what a loser."
Skater 2: "yeah i know right, that was a total shitflip."