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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.
by kcaJ sleinaD January 02, 2011
The sound of cracking a boner or being sexually turned on.
Then i turned and saw her at the bar and HNNNG! There it was.
by bash_steve May 03, 2009
The sound made when pumping out a quality dump, either through pleasure or when down struggle street.

Random dumper: So there I was...ass deep in the porcelin bowl then bam...HNNNNNNNNNNGGGGGGGGGGGGGGGGGGGG!!
by cervixsmash February 15, 2011
The term “hnnnng” (with a variable amount of n’s) is the code word for people on Tumblr with pages looking to find followers and gain friends through the popular, stranger-finding site Omegle.
Stranger: hnng
You: hnnng
Stranger: tumblr much??
You: Hell yeah!! :D
Stranger: URL?

by fuckyeahhnnnng May 16, 2010