I hate Ronda Rousey with the fury of a thousand suns. It is hard for me to decide whether she's worse or Brie is.
If you want the full experience, find the season of The Ultimate Fighter where she coaches versus Meisha Tate. I was ambivalent towards Rousey until that season, and now I'd gladly erase her from existence if presented with the opportunity to do so without repercussion.
Since you likely won't go watch that, she was a massive cunt, her trainer (maybe husband? can't remember) was possibly an even bigger cunt, she acted like she was the second coming of MMA Jesus despite having only one solid move (arm bar), she was a huge hypocrite about how to treat people, and when someone finally breaks through her cunt barrier and makes her feel bad, she's the WORST fat blotchy-faced crier I have ever seen. If you ever thought she was attractive (I never did even before this, but she wasn't hideous), seeing her sobbing will cure you of that immediately.
Honestly I'm not doing it justice, you'd have to watch the season to see her progression into cuntiness.
I have heard, in the years following the show, that she came out and said that she would never wrestle/fight a man because she'd get destroyed. I honestly thought she had said the opposite of that before, maybe even on the show, but I see that statement (the losing one) attributed to her all the time, so maybe it is actually true. If it is, then I guess she'd rank slightly below Brie on the Cunt-o-meter, as Brie would never admit a man could beat her at anything.
tl;dr she's a massive cunt