i wouldn't say it's a machismo thing as much as it is a having fun thing. my route to work is a little over three miles (kenso to washington square), so any time i feel someone on my wheel or see someone ahead of me, i know i can give almost a full sprint the entire way.
it's fun.
the other day, this kid and i (a stranger on a ss) went block for block through traffic from spring garden to chestnut street. neither of us were trying to be badass, but both of us were having fun.
when i'm on longer rides, and i'm on someone's wheel or vice versa, the idea that one of you is going to gas out first is fun. the whole bikesnobnyc bull about "stupid hipsters turning their commute into a race" is dumb. there's nothing wrong with making otherwise mundane trips into a fun time.