Dead Tube
Yakushoku Distpiari Gesellschaft Blume
Someone already mentioned that potion manga, but at least I can actually still read it...
Re:Monster - Dropped it after the elf rape dungeon and the Stockholm syndrome waifus and it's completely glossed over like it isn't a big deal at all, not to mention the ridiculous powercreep even by isekai standards.
Akarui Sekai Keikaku
Kamisama no Iutoori Ni - That ending? Hell no, do not waste your time on this or part 1.
Boys on the Run - This main character infuriated me. Do not be deceived by the the description, this is by no means a zero to hero story, he is a zero from beginning to end and he never learns.
Dolkara - How to tank your story, step one, make it so that the MC takes the backseat, step 2, add a bunch of melodrama with bad people that constantly get away with doing bad things.
The last arc of "Spirit Migration" - wtf was that? It started out so good and then they basically gave up once he escapes the dungeon.
Doubt (TONOGAI YOSHIKI) - Fuck this story, Nine Hours, Nine Persons, Nine Doors is a better story in every conceivable way (999 is a game though.) Actually, fuck everything written by TONOGAI YOSHIKI.
Skeleton Soldier Couldn't Protect the Dungeon (aka: the skeleton soldier that can't protect shit, doesn't learn shit, and an author that can't make up his damn mind chasing trends)
Any 4-koma format manga that splits the panels into 2x4 or 2x8 symmetrical boxes per page. Don't really hate them, I just find them absolutely unreadable. The anime that spawn from them have the occasional funny skit though.