When in a threesome, the act of a man's testicles slapping against the forehead of a third member located beneath the man's partner.
Roger: Gladys, why is your forehead so sweaty?
Gladys: Man, Frédéric just gave me Indian Hacky-Sack with Joanne. It was ball-slapping fun!
Gladys: Man, Frédéric just gave me Indian Hacky-Sack with Joanne. It was ball-slapping fun!
by Funny Boner March 21, 2016
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