Nikki Bella is going off on Ronda Rousey -- claiming she's done more for womens wrestling than Ronda EVER has ... and says when it comes to the sport, Ronda's the real "Do Nothing Bitch."
The two have been feuding ever since Nikki betraywed Ronda on "Raw" last week -- teaming up with her sister Brie Bella to stomp Ronda out in the middle of the ring.
Ronda told TMZ Sports the sisters were a bunch of "untrustworthy bitches" and then called them "Do Nothing Bellas" (a twist on her famous "Do Nothing Bitches" line) on social media.