I do not like to say that newbies are a pain to dive with. As an instructor I know what to expect from my students having trained them. The qualified diver that I have not dived with before worries me more, expecialy if they have been diving for a while and think they can dive. A lot of divers tend to get very complacent as they get a bit of experience. They then take short cuts!!!!!!!! That is where I find most problems start arising. They then also throw some of there training down the drain, as there friends tell them that there are better ways to do it. The friends always know more than the instructors.