A new study shows that guys mistake friendly gestures by women as sexual come-ons, and sexual come-ons as friendly gestures. Thus guaranteeing us a life of misery and solitude unless by sheer dumb luck we're tackled on the sofa by our to-be paramour. So to all my female "friends" who really were just willing me to jump them, much apologies.
Also, Ezra's right: examples of which signals were which would have been a nice addition to the article.
(Men, of course, as so tastefully commented by LitBrit, er, "wear their hearts on their sleeves", if you will).