I haven't heard of it happening lately but my first judo sensei spent quite a while in Japan in the 60s - told us/our dojo of a Japanese member of a dojo in Tokyo who let his club know at the start of a training session that he would be leaving, and training at a different dojo - I don't really remember the circumstances - whether the guy was leaving because he didn't like the dojo and wanted to switch allegiance, or because he had to move to a different city, or.. orů but - the story related to us was that the other members of the dojo essentially all had a "practice" with him, each doing his best effort to give him a good bashing, and at the end of the night, it turned out to be his last practice anywhere. Whether he died in the hospital or on the dojo floor I don't know. It may be one of those urban myths, and I may be paranoid, but each dojo and each sensei is different.
When I'm going to take on a new dojo (because I've moved - and I move a lot - coaching isn't all that stable a profession) I always ask if I can watch a practice or two before I join, and I make sure to have a chat with some of the guys in the club. So far nobody's tried to hurt me but I know it's possible. Now, I'm old enough that they probably won't bother, but around the martial arts, it's always a good idea to be careful about the "tough guy" attitude that some training locations have.
Hmm... This happened in Japan, I doubt such activity is legal here in Canada or USA, besides, if ur really getting hurt u can always walk out... And if anyone is paranoid you can always say you would like to stop training for a while and not say "I don't like you, so I'm going else where".... That's not nessasarily a right thing to say at any point, and in any country.... Just rude!
Just because one person had issues and does not like their sensei I doesn't mean that the sensei is a bad sensei, because there are many others who enjoy training with that same sensei...that's just my 2 cents