most difficult actors?

Throughout my career as a stage manager I was asked if I could work with difficult actors. The number I really worked with can be counted on the fingers of one hand. Most so called difficult actors were lovely and because there was a good team to support them, were absolutely fine. It is when the other departments fall down that some actors become a problem. I have worked with picky and actors particular about where props are, how costumes are set etc, but I don't mind going the extra mile if it means that the performance is fantastic.

'Difficult' in what sense?

But if you mean difficult to work with, I'm sure that only the people in the direct line of fire - directors, fellow-actors, costume departments, make-up artists, stage managers, runners, etc, would ever know the answer to this! And being professionals, most of them would keep this information to themselves.