When the "Engrish"/ bad grammar gets bad enough that it's hard to understand. A few small mistakes are no big deal, but when every character is referred to as "he" it starts to take away from my enjoyment of the VN.
Filler dialog and scenes. I'd rather take a small update or short game than a hundred boring filler scenes. I like great dialog but for the love of god it must serve the story and progression.
Most my peeves have been mentioned. I detest bimbo in a game. Massive cow tits and ridiculous donkey dicks. Bad translations. There is just no excuse for that. Bizarre stories (I'm looking at you Mou-Sama). Extremely unrealistic interactions between people just breaks immersion for me. Koikatsu and some anime art. Not crazy about fantasy/sci-fi genres. I prefer my porn games down to earth. If I want fantasy, I'll play Skyrim, dammit.
MC who treats women badly because he thinks he's a god.
When there is no penetration visual in sex scenes.
You cannot change the MC name. Multiple routes without option to name savings.
Story stalling.
There are couple of games that were extremely popular from the very beginning, but developer started dragging story and blueballing players by introducing never-ending small updates with no real progression. One example: Happy Summer
I actively ignore every update of those games.
now that i think about it i also dislike games that try to cater to everybody, so there's no focus and a lot of wading through stuff you don't find interesting