1. Bullshit originating from, related to, or otherwise connected to fools.
2. Usually preceded by "Fuck that-"; eg "Fuck that foolshit"
3. Originated from an online chess player from China, whom, not knowing the rule of 'en passant', saw his oppenent's pawn move behind his own and exclaimed "You cheater! That's foolshit!" Ironically, he was the one that was really full of foolshit.
"Dude, cake rules. Pie just can't compete," said Dave.
"FUCK THAT FOOLSHIT!" responded Inigo. "Pie will fuck cake up any day of the week!" Inigo then stabbed Dave and was elected President of the Earth.
Dingus: This pie is pretty good.
Lumpy: This cake is so much better.
Hesh: SHUT UP! Hesh wants SEX! Kibbles, come here and give Hesh SEX!
Lumpy: You sick?