Absolute worst (with what they had to work with): The Spirit. The insanely bad premise and script, and those serious actors chewing up the scenery, couldn't have been worse if they'd brought Buckwheat back from the dead to play Ebony.
Second: Flash Gordon. Again, an inane story and scenes that would have to be improved 500% to rate being called campy.
'Course, there was always Flesh Gordon...bad scifi/soft porn (is there any other kind), from the early 70's. Saw it on late night TV when I was 14. More of a spoof than anything else (especially given the shape of that space ship).