It isn't a bannable offense to ban something your teammate intends to play nor should it.
If I am one of the last 3 in the team to get a choice to ban a champion I can ban ANY champion I want from the game regardless of the reasons. Suck it up and pretend the enemy team blind banned your champion and do whatever you would do in that situation. Or you can be a 9 year old and decide you are going to troll and feed because you didn't get your way, I don't mind you can eat the report from the rest of the team.
Especially things like nidalee and xin zhao, I really don't feel like flipping a coin to find out if you are going to do really well or be an underfed useless nidalee or a no gank xin zhao who fails to farm up the jungle by mid/late game to be worth something.. I don't know what you guys have seen, but certain champions seem to either do very well or horribly and I'm not going to risk some guy/gal I don't know picking these win hard/lose hard champions.