Ladies what are your thoughts on this?

Back story:

My wife's best friend is extremely flirty with any and all guys she meets. It is so obvious that I almost feel embarrassed for her when we all hang out and she hangs all over our other friends who are guys, she even acts flirty towards me which has always been weird. My wife has never been concerned with her behavior and told me it was because her bf was closer with her older brother than to her sisters and identifies more with men then with other girls but my wife grew up with 3 brothers and doesn't flirt with every guy she sees, she never did even when we were just friends. My wife is a very attractive and social person while her best friend is social but not nearly as attractive looking.i also want to point out that she (the best friend) is a nice person and doesn't just hook up with guys or try to actually pick them up- just annoying flirty.

I think the reason she is so flirty is because it is her way of drawing attention to herself possibly because she knew guys were more incline to be attracted to my wife as they have been best friend since 5th grade and have done everything/go everywhere together. Do you think that could be a reason for her acting this way or do you think it is just because she grew up closer to her brother?? Or is there some other reason a girl would act this way?