I would have to say pinworn insect nate and then cat abandoner chuck. nate is the worst character but indirectly provided ments since it was cannon fodder for lenny to troll. chuck was a complete ment killer and made large parts of the early videos unwatchable.
I don’t reallt consider the losers club to be part of the genovaverse since they’re not really in any videos cucking ments so they don’t rate as highly despite them all being complete cookie cutters
If you look at the Las Vegas trip you can spot McCuck a few times in the background, probably just hanging around them and maybe carry their stuff, almost like a slave, desperate to join the club!