I get it. I am a younger sibling too and seeing Ayato, I can now relate to my sister being pissed off with me HAHAHA. Sometimes I wonder if only mc would smack the shit outta Ayato that would be so satisfying as fuck. I mean, a person can be a tsundere, I'm fine with that just don't be so annoying asf.
Totally, like he's brother would communicate and he'd be yelling or even accusing mc this and that. Like that one scene where Ayato clearly went to mc's room without permission, and when mc dragged his ass back to his own room he woke up and suddenly accused his brother of trespassing on his room. I know it's a supposedly a funny moment between a tsundere lil bro and mc, but that totally got on my nerve. Ever since then I only ever saw him as rude and disrespectful little shi— ... it's no wonder that mc would likely trade him for a good kid like his bf, Toujo to be a lil bro.
Literally! I'd do the same too. From the get go I had a dislike for him with how he treated Mc. It's funny how we getting work up by a fictional character but what can we do right, since we want to enjoy the story to the fullest without getting annoyed by characters like him trying to ruin our moods, making it so that we can't enjoy it fully
ヽ(`Д´)ノ

Man i dont really like the little brother