When one senses the arrival of a fart, allowing it a safe exit route through the bowels, but the fart is really poop disguised as a fart, resulting in shat pants.
Foop is a more widely accepted alternative to the word shart, a word made famous by the movie "Babysitter," starring actor Jonah Hill.
Friend: "I don't really feel like going into the pool right now, guys."
Friend's Friend: "Why not, bro? Just use your boxers instead of trunks!"
Friend: "Well I would, except I had a wicked foop the other day."