speeding up a bike--a way to show off?????????

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i've seen guys increasing the speed of their bikes when they see girls,well one thing i don't understand is whether they do this to flee frm them or is it a way of showing off.if it's the latter,i don't understand,y a girl wd like a guy jus b'coz he drives fast???can any guys out there reply to me plss,iam really confused..wot is the psychology behind this???????????????