a fetish or body condition in which when you exposed certain parts of your body and have the rest covered, your body exhibits arousal
Shelia has a naked hard on when she exposes her ankles.
Tim gets a naked hard on when he exposes his shoulders in a wife beater shirt.
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Being in a 69 position with the dude on the bottom wearing only a construction hard hat so that shit doesn't fall on his head
Bro: What did you do last night?
Me: After giving the Naked Hard Hat to my gf, we finally finished our 420 sex positions list!
Bro: Awesome!! *High Five*