personally i think the worst anime i've seen apart from the kiddie ones (they're intentionally bad) was Gunslinger girl

i didnt really give it much of a chance because it lost my interest in like 10 minutes, i watched the intro and thought geez this is abit boring then kept watching... and nearly fell asleep

maybe it gets better? i dunno

also another bad one (which is a kiddie one) would have to be Baybladez, i mean they moved DBZ into a spinning top game lol