While not the worst anime (and I say this from a bunker behind a shield where the stans won't find be able to reach me) Yuri On Ice wasn't that great and doesn't deserve a movie. (And while I'm on the subject of not that great, Madoka was pure shock value and actually pretty bland too)
Darling In the Franxx (specifically the second half, they could have had something great, everyone who stuck the first few eps could feel something building but nope, they decided to ruin it)
Angel Sanctuary. The anime was a terrible adaption, covered nothing, took away the beautiful detailed art style of the manga, never mentioned angels, and just blandified (yeah so bad I had to make up a word) everything.
And sorta related to the top but (I say as a mecha fan) I don't understand Gundam. I've tried to watch so many of them and they're just so boring.