I call most black belts sensei unless they correct me. I use "sir" a lot for anyone of a higher rank than me... that's admittedly a holdover from TKD more than proper Judo etiquette.
Its nice that I have been in clubs where they don't really care that much about titles.
My judo club is pretty casual, we really just use sensei when we are visiting a different school or at a seminar. This may be on account of class is almost always run by one of our nidans and none of them really like being called sensei.
Most of the students, kids and adults alike, call any black belt they see "sensei". I am starting to break that since I am not "sensei". I just tell them to call me "sempai".
FWIW, in Japan the term is thrown around pretty loosely. Really, anyone in a teaching or otherwise authoritative role can be called sensei, although I'm sure groups here and there are not without their own conventions. It's also rather uncommon to say someone's name + sensei, beyond specific addressal in a group of likely people or some formality. For actual scholarly types, the terms "kyouju" and "hakase" are usually applied, and there are specific titles for other masteries as well.
What really wigs me out is the "sensei + name" routine...
There is no per se 'teaching rank' for judo in the USA. To be a teacher you need to have coach's certification, or at least someone with it has to be present on the mat. I have it and i'm a nikkyu but there are sandans who don't.
In your case, it would be "Grand Dragon Of The Invisible Empire".
Originally Posted by Hedgehogey
I am ikkyu and senpai (senior student) and spend a lot of time "teaching". I lead warmup and drills and instruct in techniques to assist my sensei (he is not 100% physically able), sometimes running the class when he's absent.
A lot of the younger students call me sensei, though not because I've asked them to. I'd rather be a regular student, but I'm glad to assist in service.
Fwiw, I believe USJA calls Yodan and above a teacher grade.