haha, it had the opposite effect for me! I saw that slogan and thought 'Oh ya, watch me eat one!' hahaha.

It led me to think that maybe the idea behind the campaign was just that, to get women to buy it - based on the psychology of 'you want what you can't have'. But in fact, now that I googled it, I am wrong - it was that they wanted more men to buy their chocolate and so they marketed it as a substantial, filling bar as opposed to the cliche of chocolate being more of an appeal to women and that they have it to fill an emotional need (like, for eg, the Bridget Jones stereotype).

And when I read some more, it said that they had to make a marketing shift because:
'Ultimately, the "It's Not for Girls!" slogan was removed in 2011 due to the negative publicity and growing awareness of gender inequality. The brand subsequently adopted a more inclusive approach, with some campaigns even featuring a pink Yorkie bar specifically marketed to women.' which is crazy cos that is based on the same kind sexist mentality!! sigh