As a new diver I am very clear as to my skills when going out with others, so the expectation is set before we commit to a dive together. That's just good manners. But if people still want to go out, then they have to understand that I am slower to gear up (which is why I show up earlier and start prepping sooner), from time to time I may not have perfect bouyancy, and I may be anal retentive about the pre-dive discussion where I ask a million questions.
It's not fair to assume that people like me will never dive in public until we have mastered skills in our bath tub. Besides the obvious difficulties of transitioning from 12 inches of tap water to 50 degree salt water, there are finer nuances of actually propelling yourself and maneuvering.
So with that caveat my safety pet peeves are:
Senior divers who are
too comfortable.
Divers who blow off safety things like checking to make sure you know each other's gear before going out. With so many different models and styles of gear it's important to know how each other's works. For example, I don't have a standard yellow safety second reg I use my Air2 module on my BC. So it's good for people to know that they would get my reg rather than try to find my emergency reg. Same thing about where is their knife, how weights, BC or BP/W comes off, etc.
Divers who don't talk about how y'all like to be buddied up (side by side, top/bottom, in-line). That becomes a point of annoyance that makes a seemingly fun dive miserable and if you aren't looking in the right place you won't ever find your buddy in bad vis.
Not looking around for your buddy.
Embarassing someone into pushing their comfort zone.