This is a prank mostly for children. You need 3 things, Gum, A Dorky, Stupid person, & the sly person for this job.
Chew Gum on a swing waiting for a victim to run up expecting an open swing. When u see the victim run up to let the victim beat by a hair but have the gum on your hand, your hand will be on the swing. They will lean back or sit down to claim the swing; this is when u leave the gum on the seat and pull out your hand to make their back/butt all gummy.
Ex. I chose this kid named Eric; Dorky and stupid. I did the main steps and he leaned back & I left the gum. This kid is so stupid, he smeared it around accidentally and fell in the sand on his back. It was probably 4x4 in. w/ sand all over. Me and my accomplice were laughing so hard. Eric went almost half the school day w/ gum and sand on his back.