I think why we as men automatically assume that a girl is interested, is because we don't want to miss an opportunity.
Most men, including myself, really arn't out there to make friends with women. We don't see a girl at a bar and think, "She'd make a good friend, I'll go talk to her" So when a girl approaches us we feel you think the same :D[/quote
And which would you rather, have a guy that you have interest in, think that your interested in him and act accordingly, or have him think that you arn't interested in him and not give you the light of day?
In us assuming you are interested, we give you our attention.
If we are really interested and you act like you arn't, we lie to our selves and believe you are. Blame this on those women who decided long ago to begining the trend of playing hard to get. You guys just made it more difficult for us to understand, and therefore we assume you are into us.