As a fair few people have pointed out, it is most likely down to a complete lack of social contact with women. While I never had a sister, alot of the people in the area I grew up in were girls, so since I young age (even though I'm an avid gamer) I've had no problem talking to girls. From this, I've stayed friends with girls the vast majority of my life, so it continues to be no problem for me. As with alot of the retards who cannot speak to girls, this is most likely due to them being your steriotypical 'gamer geek' who spends all their time in their bedroom, never speaks to anyone when (and if) they go out, and so most likely has not talked to a woman other than their mother for several years. To these people, an average girl is a very alien thing, and so they have no idea how to respond to them whatsoever.