I'm genuinely confused by whatever it is your trying to say. Let start with the the term "tsundere" While im not a huge anime fan and only ever heard that term used every so often I assumed it meant a cold character who is actually sweet and caring internally. Even wikipedia says "depicts a character with an initially harsh personality who gradually reveals a warmer, friendlier side over time"
So if you could expand on how that is a fetish that would be great. You wrote:
"The tsundere trope is a fetish because what it's about is ignoring someone's negative emotions and then getting gratification about it."
In the panels you showed he's just hiding from Teruhashi and telepathically communicating with Aiura saying that hearing the constant internal voices is a lot for him to handle.
Him hiding from Teruhashi out of the window isn't dangerous for him, hes a psychic, he can float in the air... for his character it's not a crazy reaction. When he sees a bug he teleports across the world, when he was scared by nendo he teleported across the world.
Him telling Aiura that he doesnt like hearing peoples thoughts 24/7 and that its a struggle rather than a blessing is perfectly fine, whats wrong with the author writing that? The whole point is that he's a super gifted psychic who has insane abilities that most people would love to have but he hates having them because it makes his life difficult, thats why its called "The Disastrous life of Saiki k". His struggles with his abilities should be shown.
No one can hear his internal thoughts and no one knows that he's inconvenienced by his powers. The people that know about his abilities don't know the struggle that comes with them because Saiki never really shares that or they cant understand because how could they possibly understand??
The author takes Saiki's emotions very seriously and portrays them as such, like how Saiki cared for Akechi from his childhood and lost control when he was being bullied and how he loves his friends and secretly tampers with their lives to help them. How he's scared and paranoid he will hurt them or that their friendship just wont be the same so he distances himself. He's a very well rounded character. Any minimisation of his emotions are done on purpose to show that Saiki doesnt like to be vulnerable which just adds further depth to his character.
Moving on...
"This use of the tsundere trope is unacceptable. If you can use it to basically ignore everything that Saiki says, this gives a very bad idea of a relationship. I think that this is even harmful because it is promoting bad relationship advice."
What relationship advice lol?? That panel was meant to emphasize how Saiki avoids Teruhashi. No one is thinking that he's interested in her and it's clear at this point of the animanga that he wants nothing to do with her. He thinks that she's just going after him because shes obsessed with the fact that he has absolutely no reaction to her, not because she actually has feelings. Later on however, he realizes Teruhashi has come to like him just for him, that her feelings have moved past just wanting him to find her attractive. And then he grows to respect her unwavering confidence and how she really does have a good influence on the people around her even if she has selfish motives.
The point is they GROW to actually be more compatible for one another throughout the plot. At that point in the panel they were not meant to depict a good relationship. Do you think just because the author is hinting at them being a couple they have to act like one?