I've rated a very few shows under teh score off 3 - and i am not sure if they was that bad. I might enjoyed some more today. All of these are completed - while i've a whole list that i dropped. My medianrate i around 7.

Nr1 worst anime...
School Days!

I hated it, but for what reason i dont remember - but also one of teh first 50 i saw. I know that teh anime community haev different opinion of this - some say its teh worst anime while others like it. Its based on a VN i think - and i assume its good.

True Tears
Myself; Yourself
Shigurui (Samurai are cool, but this was sooooo slow and boring)
Azur Lane (havent played teh game so it was a mess)
Goshuushou-sama Ninomiya-kun (maybe this was good? Looks OK!)
Kimetsu no Yaiba.
Ansatsu Kyoushitsu
Kämpfer
B-gata H-kei
Ichiban Ushiro no Daimaou
Gate: Jieitai Kanochi nite, Kaku Tatakaeri

Some off these are old and might need to be revalued, but eh - trash!