Do you mean like bad in the classical sense? Like apple family massacre were they got the anatomy wrong in their gorefic? I mean, if you are going to write a gorefic, get the anatomy, and description of internal organs correct. And as for just lazy and terrible, any OCxMane6 clopfic is terrible.
But for my personal worst, FoE. Prose so purple it broke the carrying capacity of the ultra violet spectrum, a chapter structor with no consistency, a main character who either bored me or pissed me off. And their entire journey/plot was a copy paste of fallout 3, with some fallout 1 and 2 elements thrown in, and just painted pony.