plural form: Happy Cacti
When a guy who has participated in "No Shave November" goes down on a girl to eat her out. The rubbing of the stubble against her vagina would be analogous to a cactus rubbing against her flesh. In an added twist, the female has a deflated balloon inserted in her vagina. As the balloon is blown up by the male partner's mouth play, the balloon expands, causing a tickling sensation.
In a male-to-male variation, substitute the vagina for an anus.
Mitchell's boyfriend made him scream out in pain and unexpected delight as Mitchell was surprise Happy Cactus'ed.