What's the worst movie ever made?

Was recently talking with friend Frank about Kurosawa's The Lower Depths, which we agree is probably the worst movie we've ever seen - not the worst movie ever made, because that would be something we'd never see - but a great movie that is actually horrible, unwatchable (maybe my first judgment was wrong - I saw it about 35 years ago - but I don't want to see it again to find out). A movie with great ambitions that fails miserably is far worse than a movie with no pretensions that at least hits its mark. The Israeli film "Lebanon" falls into the great (or at least greatly ambitious) movie that's almost watchable. It's far from the torture of The Lower Depths in that it's only 90 minutes, but it's 90 minutes of misery. And yes I get it - that's the director's (Maoz?) aim: he puts us right into a tank in the Israeli army, invading Lebanon, and almost the whole movie takes place inside the tank - replete with a rotting corpse, a terrified Syrian prisoner, leaking oil, fumes, heat, debris, sweat - we see it all, and almost everything we see outside is through the gun sights. There's a lot of tension among the 4 men in the tank, and the story hinges on the failure of one to pull the trigger at a crucial moment - we see the difficulty and futility of war, the danger at every moment, the clash of the personalities, the breakdowns. It really sounds great as I describe it, but it's so hard to watch that I can't recommend this movie. The obvious comparison is with Generation Kill, which is much more character-driven and broader in scope. Lebanon is a powerful indictment of - something - but what exactly it indites I can't be sure: war? Israel? human nature? cinema?