fisty biscuit
The act of shoving your hand up another's anus and tickling their insides while yelling "fisty biscuit!"
"Dude, my girlfriend wanted me to fist her last night, so I gave her a fisty biscuit!"
"I shoved my hand up this kid's asshole, then pulled it out and called it a fisty biscuit"
"I shoved my hand up this kid's asshole, then pulled it out and called it a fisty biscuit"