Today I bumped into a Sensei from my Dojo (One that assists in teaching my class on occasion) during the course of the workday. (We were both at a mutual customer's plant) I said hello and shook his hand with a few non MA pleasantries and did not address him as Sensei.

Would this be expected or is it concidered disrespectfull? (My thoughts were that perhaps some don't wish to be identified as such if they like hovering under the radar.)

I think it depends on the organization. I would as the head instructor at the club what he considers appropriate.

I personally would have done what you did.

yes you did the right thing, Every now and again I see my sensei at the shops or something. I just greet him like another friend, and then go on my merry way.

although i would love to see some one walk up to their instuctor in the shops, say a greeting in another language loudly and bow in front of them...would be a classic.

Traditionally only the head instructor is addressed as sensei so technically you are in the right if you addressed him by Mr. so and so.

I don't expect my students to call me sensei outside the dojo or other karate related event. However many do just out of respect. I did with my Shorinkan sensei and a 8th dan from Pittsburgh that is one of my instructors and advisors to my system.

I think you did the right thing by way of greeting him, i think i would do the same. I think there would have to be certain guidlines though. Like i don't think a student should smoke, swear, or get blind drunk (or whatever) in front of a sensei outside the dojo.

Something else i wouldn't do is sociallise with my sensei, i couldnt imagine myself doing that to be honest. But being on friendly terms in the street is ok i think.

This sort of thing really depends on the type of instructor you have. Some of them have no problem with imformal greetings and use of name. Others are more traditional and prefer a more respectful and formal greeting. I usually use Mr. or Sensei when I see my instructor around town. I leave it to him to show me how informal I can be outside of class.

I would say you acted appropriately. You were in a bussiness setting at a customer site. Associations outside of work should always be kept outside of work especially in regards to customers.

When on rare occasions wher I have run into my sensei (ie.. grocery store, deli, bakery ect....), I would greet him hi Sensei how are you? Hows the wife and kids ect.....

It just depends on the instructor as to what you should do. I think you did the right thing, and if he didn't make an issue of it, I would say you are ok.

I agree with most people so far. It just depends on your school and your Sensei.

For us we bow our heads slightly and say "osu" as a sign of respect, if it is our sensei, or a master. If it is any other karateka bow our heads slightly and say hello.