I have extremely temperature-sensitive nipples. A slight breeze blows by and the girls stand up like doggies begging for bacon treats. Which invariably makes Mr. Kitt's eyes light up. Every single time. I could have been shivering on the deck of the Titanic and he would have noticed my nipples getting hard in the cold. Seriously.
My inner comedy stage sports a bewildered Seinfeld: "What is up with that?!"
Look, I know there's some association between hard nipples and arousal and all... and yes, my nipples get hard when they're played with and sucked. But in public? You guys... if I'm out in public, my nipples get hard from temperature change, not arousal. If they're not being directly stimulated by, say, rubbing against my shirt or bra for some reason, there's just no nipple action going on. I don't think my nipples have ever perked up because I was turned on by some guy checking me out. But why is it I get the feeling the guy in the other booth just wouldn't believe that?
To quote Mandy Patinkin from Princess Bride, "I do not think it means what you think it means!"
As a woman, I'm much more subtle about my arousal than men. I don't have to worry about a hard penis popping up to say hello when I see something that makes me feel a little randy (or just because I bite into a peach or something...) And when my nipples get hard in public, it's usually a physical response that has little to do with arousal. (Really, guys. I swear.) If I get a little wet, no one's going to notice except me.
Arousal, though, is something men seem to want to be able to gauge concretely in women. They like to see the hard nipples - physical proof! Loud moaning (or even screaming) orgasmic bliss is welcome - she really likes it! And the ultimate proof, of course, is the squirt. There are thousands of web sites devoted to the subject. Except... I hate to break it to you... most of those cases (at least, on screen) are as fake as Sally moaning and slapping the table across from Harry in that infamous diner where everyone wanted what "she was having."