Rescue Dawn will get them hooked, especially if they're boomers. After that, you can blow their minds that that was the work of one of film history's great documentarians. Show them Lessons of Darkness. Most people have a visceral response to that imagery as it was not covered well when it occurred. You could start to delve into his Kinski era stuff after that, the obsessive narratives. He has more contemporary documentaries that are like watching nature specials to follow.