The human nipple is a strange beast. Depending on the context, this “small projection of skin containing the outlets for 15-20 lactiferous ducts arranged cylindrically around the tip” has been marketed as alternately sexy, obscene, artistic, disgusting, and even sexier.

But as a consumer of nipple shots, such versatility can become confusing. It’s often difficult to know the socially acceptable reaction to every stray projection of skin that catches your eye. Should you high-five your buddy or vomit discreetly into your hands? I’m here to help.

Taking a page from our friends at the Huffington Post, I’ve compiled some photos of famously exposed nipples—-complete with “NSFW Zoom” (Not Janet Jackson, she’s too obvious). First, review the Guidelines For Socially Acceptable Reactions to Nipples. Then, check out some Famously Exposed Nipples (NSFW-Zoomed into focus) and see if your gut response to each biological structure is in line with society’s nipple norms.

Guidelines For Socially Acceptable Reactions to Nipples:

* All of a woman’s breastrevealed except for the nipple, which may be obscured by clothing, hair, or paint: sexy.

* All of a woman’s breast revealed including the nipple: sexy; obscene.

* Renaissance-era artistic rendering of a woman’s breast including the nipple: art.

* All of a man’s chest revealed including the nipple: null. Unlike female nipples, which are either HOT or TOTALLY GROSS, male nipples are just there.

* All of a woman’s breast revealed including the nipple while breastfeeding: not sexy; not obscene; to some, however, still totally fucking gross, far more disgusting than a normal female nipple, whose only reproductive function ought to be arousing you on-sight (Note: it is not yet socially acceptable to take photos of women breastfeeding in public in order to engineer “gotcha” nipple slip headlines).

* All of a woman’s breast including the nipple, which the woman inadvertently flashes for the camera (also known as a “nipple slip”): sexy; obscene; still, manages to maintain the relative innocence of the woman who has inadvertently revealed the nipple, making the it that much sexier; unless of course it is Pamela Anderson’s nipple, in which case the nipple slip is simply very obscene and not sexy at all, because Pam Anderson is agreed to be too slutty to pull off the treasured nipple slip dynamic.

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Famously Exposed Nipples:

A. B.

C.

D.

E.

F.

G.

H.

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Socially Acceptable Reactions to These Nipples, Revealed:

A. Natalie Portman‘s nipple slip: sexier. SUITABLE REACTION: High-five.

B. Pamela Anderson‘s nipple slip: obscene; not sexy. SUITABLE REACTION: Vomit discreetly into hands.

C. Lindsay Lohan‘s nipple, obscured by hair: sexy. SUITABLE REACTION: Retweet.

D. Ian McKellen‘s nipple (male): null. SUITABLE REACTION: Curse your “celebrity nipple” google search for leading you astray.

E. Lady Gaga‘s nipple: sexy; obscene. SUITABLE REACTION: High-five.

F. Beyonce‘s nipple slip: sexier. SUITABLE REACTION: High-five.

G. A Real Housewife‘s nipple slip, obscured by clothing: sexy. SUITABLE REACTION: High-five.

H. Mona Lisa‘s nipple (rumored): art. SUITABLE REACTION: Scratch chin.