Impressive, a thread about the worst F1 drivers and no mention of Al Pease.
Al Pease entered the Canadian GP from in 1967, 68 and 69, driving an Eagle T1G. In 1967, his car's battery went flat on the far side of the circuit. Despite the rain, he ran back to the pits, got a new battery, ran back to his car and fitted it himself, then eventually finished the 90-lap race, 43 laps down.
In 1968 he didn't qualify, his fastest lap being 15.8 seconds off the pole time and 8.4 seconds off the driver in front of him.
In 1969, he was disqualified on lap 22 (some 25 laps down). The Matra team boss had lodged a protest with the organisers because Pease was too slow.
I think that's pretty much the worst F1 performance ever.