Why do guys always go for the most indecent girl?

Like me and 3 friends were at the mall and started talking to this group of girls. 3 of the 4 were absolutely beautiful, the other one, Christie, was ok, nothing special but she "let it all hang out" and the whole time all she did was talk about how horny she was and how much she wanted to "do it". After 3 hours 2 of my friends were following her around like they were dogs and she had food. My third friend had a girlfriend so he really wasn't to interested in them. I looked at the other 3 girls, and only one of them was sort of like christie but she had the decency to dress nice and not talk about s*x all the time. The other 2 i talked to and they both seemed really nice, they both kept the conversation pg and I was stunned they would hang out with someone like Christie. They were both so nice and dressed better then a lot of girls I know. Within a week of knowing Christie both my friends asked her out, one was turned down the other she said yes to but then they broke up when my friend found out she was dating another guy. Why do guys do this, I'm a 14 year old guy and I find those kind of girls an insult to our society. I'm not sure why they all go for the most indecent one, why?