Girls, what's with the inches and the sad face posts?

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Last week, some of my female friends at facebook post a number with inches right next to it and followed by a sad face [ 5" =( or 5 inches =( ]. I was kinda curious about it since only female do this kind of posts, so I tried to search the web and found out that it has something to do with the breast cancer awareness thing. The rules are quite simple, just post the size of your feet and put a sad face after. In that way men will be curious and think of it as a naughty post. Uhmm, in a way, yes. It looks naughty and dirty. Coz men will understand that kind of post as your partner's penile size and the sad face means that you are not satisfied with it. Well my question is this, how will it contribute to the the breast cancer thing if you post this one? Posting your foot size with a sad face, what is the relevance of it to the breast cancer? I'm just curious about it. =)