The Art of Brian
I can imagine how the idea started: the Monty Pythons sat down one day & watched a whole raft of over-serious, pretentious, boring 'Life of Jesus' biblical movies, especially Jesus of Nazareth (which came out only a couple of years before Life of Brian), King of Kings, The Greatest Story Ever Told, etc. and thought, there's a rich vein of 'sendupable' humour here just waiting to be tapped. In hindsight I'm just amazed that no one had come up with the idea before, that these Son of God 'bore-fest' flicks were ideal fodder to be satirised, because the tired, hackneyed original ones were often (unintentionally) funny in themselves!
I knew when Life of Brian had made it ... had transcended the merely funny-for-funny's sake and become something akin to literary art. It was in the mid-1980s when my usually ultra-conservative and risk averse English Lit Department at university put the Life of Brian screenplay onto the syllabus of 100 level texts to be studied - alongside a lot of dusty & unexciting old novels and plays. That was something a bit revolutionary back then!