2006's news (Score 1)

"As studies show, and many women will attest, men tend to misinterpret innocent friendliness as a sign that women are sexually interested in them. Dr Haselton and Dr Buss reasoned that men who are trying to decide if a woman is interested sexually can err in one of two ways. They can mistakenly believe that she is not interested, in which case they will not bother trying to have sex with her; or they can mistakenly believe she is interested, try, and be rejected. From an evolutionary standpoint, trying and being rejected comes at little cost, except for hurt feelings. Not trying at all, by contrast, may mean the loss of an opportunity to, among other things, spread one's DNA."

Don't misunderestimate yourself: Why people think that rivals are better looking than they really are http://nomadlife.org/2006/11/dont-misunderestimate-yourself.aspx
(pirated from The Economist, November 2006)

Conclusion: In order to avoid hurt feelings, cute girls should never smile.