In the eyes of the law..can a woman rape a man?:
Legally yes it can and has happened. The imfamous urban legend of Biker chicks knocking a guy down and having thier way with him in a park is an example. 

The reality is that it's hard to have unwilling sex with a guy by deffinition. Guys like sex. If they are not in a relationship they have  little incentive to avoid sex, even bad sex. 

A guy weak enough to be "raped" would be a laughing stock. The most likely scenario would be a date rape drug and the guy contracts an STD from it's usage. Especially a married or engaged man. However it would be extremely hard for the guy to prove his unwillingness and it would take a mountain of evidence to prove such.