Have you seen how ripped Rousey is? She has got neck muscles that could handle a punch way more than the average man.
Maybe so but Mayweather is far from being an average man. I have seen women who were bigger and stronger than Rousey and could bodyslam the average man without difficulty but they would not have been crazy enough to challenge a male professional boxer, not even a featherweight and certainly not one in the 150 pound range. If Rousey really thinks she can beat anyone on the planet in a no rules fight she is exceptionally delusional. There are women who can beat her, they just don’t fight professionally. At least she hasn’t met a professional who can, YET.