All of them? But if I have to narrow it down to two votes, it's the loli characters and the harem bullshit.
I absolutely fucking hate infantilised female characters. You know the kind. They look like a child, dress like they want to put me on some list just by looking at them and they have a distinct mannerism that the creators so desperately want us to think is cutesy but I think is repulsively creepy.
Oh what about the moments where the male hero finds himself in an accidental situation with a female character and she responds in the most predictable, tsundere way possible by calling him a pervert and never letting go of the grudge until a torturous dozen hours later or so?
Of course we must always have a womanising guy who loves to drink, party and gamble who thinks he's suave and has a way with words but is just a creep who looks like the poster boy for why we have the #MeToo movement.
Overly exaggerated anime body movements utterly get on my nerves. The guys can act fairly normal but the women? Oh she'll be bending forward in the middle of a conversation suggestively while the camera deliberately pivots to right in front of her. Maybe she'll tilt her head to the side to be cute and do that thing with her arms like she desperately wants to twirl on the spot.
You can also be a murderous, psychopathic bastard but the story still seems hellbent on redeeming this character, damned the consequences both thematic and moral.
Don't you dare hit the age of 30 because now you're considered an old timer. That joke about you being a cranky old man whose back will give any day now will certainly never be a dead, beaten horse.
Honestly, I think the genre should be razed to the ground and rebuilt completely. It's not going to happen anytime soon, unfortunately. Fuck, I think the Trails series hits every note mentioned in this thread.