Not to generalize or sound sexist, but...
In my own experiences (yours may differ).....
Male co-workers are more honest and competitive when it comes to working towards a promotion.
Females are more backstabbing, brown-nosing, tattle-tale types that'll start rumors about men to get ahead of them.
I blame genetics. In a world dominated by alpha males, females need to abuse any possible advantage as leverage. It's not fair, but hey... we pee standing up and they have multiple orgasms.
