with specific regard to people who avoid training with beginners
We've segmented our classes and now have a formal beginning class. It's alleviated a lot of the pain of spending the whole night with low level kyu ranks. This was actually a major issue at one point with some serious frustration on the part of the senior folks. Otherwise, I understand the point.
people who can't shut up and just train
I'm an inveterate bullshiter but I'll also get down and train. I shut up as the practice gets more intense.
people who ignore the technique demonstrated because they learned to do their sankyo "this other way"
Everyone does this and in every dojo I've ever seen. Our dojo is horrible I've seen kyu ranks correct dannage before. Actually, the one time I'm thinking about the kyu rank was right.
I dunno how much of an issue this is but I'm in strange world most of the time.
indeed people who apparently are too important to tidy up the mats after a class. (I'm not talking about people who fold their hakama up first, I'm talking about people who just slink out of the way and chat.)
There are times when I don't put away the mats. Then again, this is usually when putting them out was a one man job and I was feeling bitter about that. Again, overall a non-issue for us.