No, this is not the start of a bar joke. It really happens in the video.
Three guys - a rabbi, a priest, and an atheist - smoke marijuana together and talk about spirituality and religion and each other's beliefs. They also talk a bit about how marijuana fits in with their religions and the world they live in. It ends with all three of them blessing each other.
WARNING: This video features the use of mind-altering drugs which is unlawful in some places.