Short for genitals. Only exists in plural form, as there is no such thing as "a genital".
I was really nice to her, so she let me touch her gennies.
(Noun) A synonym for the "genitals." Can be used in reference to male or female genitalia.
"Ohhh, touch my gennies, now ya hear!"
"I've got the crabs all over my gennies."
"I'd like to get to know her gennies real close like, I reckon."