giriasis

I am going to agree with Janet. I think your sensei is trying to make a point about reliability. He knows the 5th kyu will show up so he asks the 5th kyu to teach.

As far as etiquette is concerned here are a few situations I have been in.

First example:

Sensei can't make it that day and calls the dojo. The highest rank on the mat at the time that Sensei calls is a 3rd kyu. He asks 3rd kyu to teach. I was currently ranked 1st kyu at the time, I show up about 25 minutes into class, 3rd kyu asks me if I want to teach, I say, "no, you already started class so please go ahead and finish."

Second example:

Sensei is out sick and had made arrangment for instructors while he is out. Each of us dans and some kyus, are given a time slot to fill in for sensei while he is out sick. Saturday second class, it appears that the instructor is not showing. All the dans stand around and ask each other who will fill in. I volunteer. Right at the time when class is supposed to begin, the selected instructor, a 2nd kyu, shows up. He says, "oh no, you're higher rank, why don't you go ahead and teach. I say, "no, since sensei asked for you to teach you teach." 2nd kyu proceeds to teach.

Third example (just happened today):

I was asked by sensei earlier this week to teach the 2nd class on Saturday. I'm a freshly minted 1st dan. 2nd dan of about 3-4 years shows up. Awkward that I would be teaching a sempai, I ask him to teach. He says, "no, sensei asked you to teach. I showed to take class and train. Please teach." I proceed to teach.

In each of these instances, someone lower ranking was requested by sensei to teach. Each lower ranking person requests that the higher ranking person teach in order to defer to higher rank. However, higher rank person defers to sensei who selected the lower ranked instructor and tells lower ranked person to go ahead and teach.

So the rule in our dojo is if sensei doesn't show up and does not select someone to fill in for him -- The Highest Rank Teaches.

However,

If someone is selected by sensei, that person teaches regardless of who else is higher ranking. Most of the time the lower ranking person will ask the higher ranking to teach, but the higher ranking person still should respect sensei's request and tell the lower ranking person to teach.

That's it. It's nothing personal and no questions asked. Pretty much sensei will ask people to fill in certain classes, he starts from the highest ranking and goes down the list and also considers who might be there that day. In the 1st situation, I was never really reliable to show up on time and on a regular basis enough to be considered to teach. It was nothing personal and the 3rd kyu taught a great class.

If it really bothers you that much you need to talk to your sensei about it in private, but don't just complain come up with some solutions, i.e. offer to help create a list of all the higher ranking folks who would be willing teach and the times they would be available to teach.