A fork of Rural Dictionary
The phrase "hnnng" is a form of onomatopoeia used in context when a person sees a very sexually attractive person of the other gender, or same. I personally like to think of it as the sound a young woman makes just as she feels her ovaries are going to burst from being over exposed to excessive sexual hotness. It helps to sound it out. "hnnng-ahhh" I like to add the gasp at the end for I know that's what those fine young mistresses do when they see I have walked into the club.
Girl 1: "omg look that sexy guy from school walked in!" Girl 2 turns in dramatically slow fashion, and locks eyes with Sexy Guy. Girl 2: "Hnnng" Girl 1 must now proceed to fan Girl 2 as she recovers from the sexual trauma her ovaries just endured.