Re: Leaving the Dojo
In the fifteen years my dojo has been open I have had three ot four people approach me with similar complaints who wanted to join our dojo. In every case the student turned out to be a problem. They had inflated ideas of how good they were and how hard they had trained. They were coming to me because they (mistakenly) thought I might be an easier way to get ahead.
In one case, I had a student come and train with me and he recounted his relationship with his teacher. In that case I felt that he would be justified and much better off to have left his teacher yet he didn't do so. He has remained a senior student of this teacher to this day.
So, it is impossible to say from the info provided which kind of student you are. But with this in mind, I wouldn't go into a new dojo and tell the teacher that this was why I was looking to join. This is just like going to a job interview and telling the prospective employer what a jerk your former boss was and how you couldn't get along... Danger! Danger! Danger!
If someone in this position is indeed leaving for the reasons mentioned, the appropriate thing to do would be to give back the certificate (you don't want to have a certificate from someone with whom you don't want to be associated), write a thank you letter to the former teacher thanking them for all their effort, deliver that letter in person and inform the teacher of your decision to leave and then go train with the teacher with whom you wish to be associated. There is no need to go over the reason for your leaving with anyone (just as you wouldn't in a job interview or if you did you'd stick to the standard bromides like "looking for greater opportunity and increased responsibility".
It sounds like the Aikido community in which you live is small. Don't make things hard for youself by developing enmity with any teacher. If the old teacher starts to bad mouth you, it will only reflect badly on him if your behavior has been approriate. The secret is to make sure that you are a model student at the new place.