What I expect from other divers depends on whether or not they're diving with me.
If they're not diving with me, about the only thing I expect from them is that they not interfere with my diving experience. In other words ... don't destroy the visibility or environment through poor diving techniques ... don't poach or disturb a subject I'm taking a picture of ... and don't be stupid or inattentive to the point where your actions affects my dive. Other than that, I don't much care what you do.
If they're diving with me, there are some additional expectations revolving around sticking to the dive plan and following acceptable buddy protocols. Those will really depend on both the diver and the dive. I expect far less from someone who's new, although at whatever level I do expect my dive buddy to take the dive plan seriously and make their best attempt to be a responsible dive buddy.
That's about it ... we go down to have fun, and as long as both of us are doing that, I can be pretty flexible with how they're doing it ...
... Bob (Grateful Diver)