My nomination for the worst film ever is 'The Limey' starring Terence Stamp. Pretentious and 'arty' in the worst possible way, incredibly silly dialogue and holes in the plot the size of an asteroid.

Mr Stamp plays a London gangster who goes to Los Angeles to investigate the death of his daughter. At one point he gets himself badly beaten up and only then reveals that he's carrying a gun! In another scene he and a henchman kill someone at the villain's mountain top retreat. They are then chased down the mountain by the villain's lieutenant. Meanwhile we are taken back to the retreat where the cops have arrived after failing to notice the car chase and mayhem that they must have passed on the way up! There is another excrutiating and unconvincing scene where Mr Stamp talks to a mildly puzzled Californian detective in impenetrable Cockney rhyming slang for no very good reason.
It's as bad as any 50s B movie - but there aren't even any silly monsters to laugh at - not a 'lobsteroid' in sight!