Re: Who to call "Sensei"?
We tend to call anyone teaching sensei but only at the time they're teaching, so if i'm teaching I'll get called sensei, if someone else is teaching then I'm just John even if it's 'my' class and I ask someone to show something - they're referred to as sensei and I'm John again until the class moves on.
Some people call me it all the time, even off the mat which is a little funny and feels very weird to me... One of the guys from the club came over to my house one night to have a chat and just hang out - he bowed to me when I answered the front door and said hi sensei and bowed when he left. Still makes me laugh and he still does it.
It just feels right to refer to a Japanese teacher on and off the mat as sensei, but not a western teacher for whatever reason. Just feels awkward. There have been exceptions mind you - with Bill Smith and Haydn Foster then it always felt right to refer to them as sensei.