I worked a lot as a background actor on many movies and TV shows. Most actors came across very professional and serious about their work. As background, we don't get to interact with the actors too much, but you can get a very good idea about them by direct observation and how they interact with the crew and background in their scenes. Again, most were no problem. But, a few stood out, either as being egregiously bad, or surprisingly great. One of the worst was Vince Vaughn. OMG, what a diva. Made everyone's life on set a living Hell. He constantly berated the crew, the director, background. Would be late to set, making everyone wait for hours (sometimes in freezing cold). Conversely, two of the best were Tom Cruise and Ryan Gosling (different movies). Both were super nice, made a special effort to thank the background actors and crew, made everyone feel at ease. Also in that category is Ben Affleck. He personally shook the hand and thanked the background actors for their work. You could tell the crew liked him, too.