Women check out other women. It’s one of the universal rules of femaledom, habitual in frequency, inherent in daily interaction, intrinsic to our Darwinian struggle to eliminate competition and nab all the hunter gatherers we can. Call it shallowness, vanity, instinct, or a product of our “beauty is God” culture, but it’s the truth. Every time a woman hails a cab, climbs an escalator or buys a mocha latte, she is being scrutinized and compared by countless female eyes. Entire industries have based their existence on the guarantee of female competition – designer shoe labels come to mind – and the media, particularly womens’ magazines, have carved the “Check-out” into a fine art.

We learn to check out at a young age, junior high dances and Friday morning assemblies spent enviously scrutinizing the popular girls lolling against the wall in their slap bracelets and J. Crew cable sweaters. Our techniqes are honed over time – the sidelong glance, the bored stare, the exaggerated up-and-down – until we can pinpoint every oversized belt buckle, brassy hair color, stiletto print and eyeshadow shade in one 5-second glance.

Men are typically ignorant; they neither notice nor comprehend the speed and depth of female surveillance. But occasionally they’ll shake off their own ingrained T&A-gazing stupor and awaken to the reality of estrogen stealth.

Boyfriend often surprises me with his check-out cognizance. He’ll notice the side looks and disapproving scowls from other women while I’m busy scratching my nose and staring into space.

“Why is that girl glaring at you?” He tugs at my elbow.

“What?”

“That girl standing at the end of the car. The whole time we’ve been standing here she’s been glaring at you like you’re Saddam Hussein. Do you know her or something?”

I glance casually down the subway car at my adversary. Her check out must be blatant for Boyfriend to have noticed, and the lack of subtlety marks her as an amateur. The minute she catches my return stare, her eyes dart guiltily toward a middle-aged businessman poring through the “Post” Sports Section. I’m now free to conduct my 3-second inspection. Results: dirty blonde hair, roots showing, done in single process where it really should have been highlights. Her breasts are round and hard – obvious push-up bra, likely Victoria’s Secret from the shape. Full makeup – foundation, copious blush, filled-in eyebrows, carefully lined lips. Low hairline, nice nose (the tip a bit too round and pert to be natural) and well-spaced light brown eyes. Her conservative dress – open khaki trenchcoat, likely Banana Republic or one of those other assembly-line business attire factories, gray dress, too-dark pantyhose that turn her legs an unflattering cocoa, nondescript black leather heels and bag – mark her as a corporate type coming home from work. No Blackberry or laptop bag on her arm- likely not a banker or lawyer – and no diamond adorning her left hand. This is unsurprising; women sporting wedding rings rarely check out with the same intensity as their single peers. The ring solidifies their win; they’ve secured a mate, procreation and social superiority are ensured, they can let their guard down. Unless, of course, they encounter a woman waving an even larger diamond. Then the eyeball-fireworks can be spectacular.

“Her boobs are fake. It’s all push-up bra. And possible nose job.”

“What?”

“You heard me. Isn’t this our stop?” I take his hand and we file out of the car onto the waiting platform.

“You can tell all that from a split second look?” His voice is incredulous.

“Welcome to the world of being a girl, sweetie.”