Why is almost everything a competition?

I can understand a little friendly rivalry with sports, video games and all that stuff. But why and how did getting at a girl become a race? My friend and I happen to be liking the same girl(somehow I'm very open with him about this), and he's talking all this sh*t with me about calling dibs, who gets first shot at her, etc; the kind of talk that would make it seem that she's some trophy and if one of us fails the other one can swoop and take her. I can't stand that kind of mentality. It's like one second we're just messing around and having fun, then it turns into Ok, u get the first go, if u fail - too bad. The guy is one of my best friends, once this girl got in the picture I feel like he's viewing me still as a friend, but also someone that he has to knock off to get the W.