What makes you drop a novel?

Bad transitions into plot armor (aka, author does not give plot armor to the MC in a smooth fashion and makes it either appear out of nowhere or just throws it at the MC)
Bad MC decisions (given that the MC is mentally capable of thinking through his actions yet does stupid things, that is unless it is for comedy sake)
Too many girls (self explanatory)
Girls with no individuality (also self explanatory)
MC's waifu is constantly targeted (like wtf the second the waifu is safe and with MC again, another villain literally walks up and kidnaps her again. That happens way too often)
Second chance novels in general don't appeal to me especially when they overuse the "oh I remember every little detail that's going to happen" kind of plot.
Novels where they put a girl in for the MC just for the sake of adding a "subtle romance" tag. Then they forget about her for the rest of the novel.
I have a lot more, but don't really feel like listing it all out. 

Untranslated words, onomatopoeias, and childish writing does it for me 

Bit sad when any novels are like are far ahead only in MTL 

harem,romance,slice of life, "BuT I CaNt kIlL HiM ThAt'd mAkE Me tHe sAmE" and mcs who start off pragmatic and calculating but then their personality becomes that of a coddled 15 yr old over the course of a story 

I drop it if I can no longer stomach the plotholes and stupid views the author is insinuating. Don't be too idealistic and realistic, machiavellianism is shit if you go overboard. 

Bad translations  Either in the traditional "ALL YOUR BASE ARE BELONG TO US" fashion or  "onii-senpai makes my heart go doki-doki" hyperauthenticity. Tale of Demons and Gods read worse than a machine translation. A lack of consistency. It's very important for an author to check themselves and make sure all information lines up. Legend of the Mythological Gene couldn't keep anything straight and constantly contradicted itself.Unlikable MCs. This is self-explanatory  Li Yao of Forty Millennium of Cultivation is an example of someone I don't want to read about.

This is just off the top of my head I'm very tired 

I dunno, I've read some good/decent CN novels that involved SENSIBLE face slapping. As in, if you publicly humiliate me, I'll publicly humiliate you. (Eye for an eye.) And in those novels, there's also some reasonable explanations for the face slapping that goes beyond "I transmigrated here so I'm taking on my host body's grudges FOR REASONS(tm)". So I know that CN novels can do face slapping well... if the writer is inclined. 

Characters without consistency.