I would agree with most who've posted that these are just the folks that fill each dojo, and we just learn to accept and deal with them, Except the thief, who I do think should be asked to change his ways. Why? because I do not see it as the green belt is stealing the right to teach from sensei (as some implied), or time, but he is stealing from the white belt the chance to learn. I think Aikido is best learned by carefully watching, feeling, trying, experiencing. Even if the green belt really understood what to do, and could really teach it, to keep stopping the white belt from trying and experiencing on his own is stealing the most important part of Aikido training from the white belt.
Even when I have my very favorite senseis as a partner, I want to try it on my own. I'm grateful if I'm not getting it by the 8th try or so that a hint is given, but they give only a hint, and don't stop training in order to say the 3-5 words max they want to say. But they give me time to try several versions on my own. Funny it is the junior students who want to stop and teach; the senseis (when they are students in another's class) generally want to shut up and train.