Disclaimer: some of the dialogue is from the episode 4x19 so I didn't write that:)
Blaine had never really understood the other glee kids' infatuation with the famous(or infamous) teachings of Will Schuester. Before he'd even set foot in the halls of McKinley, he'd heard them saying he was one of the best teachers they'd ever had; kind, encouraging and best of all, accepting to everyone and anyone that walked his way.
It's not so much that Blaine thinks he is an inherently bad person; it is more that he thinks he makes too much of a big deal out of being a good person. Within his first week of having him as a teacher in the little choir room, he was already wishing he was back at Dalton a bit. Maybe the fact that he actually wanted to pass Spanish was also a factor, and considering Mr Schue could barely speak a word of the language that probably wasn't going to happen.
But still, he understood that he wasn't that bad.
He thinks it's a little strange that the kids in the club are allowed to be so involved with a teacher's personal life, for example when they helped him to prepare to propose to Emma.
But still, he brushes it off as he understands the strength of his friendships with the original glee club.
Not to mention, he was pretty angry about how nothing had been done after the incident with Sebastian. As the teacher in charge, it should have been his responsibility to make sure that those who were at fault got punished. He cared about how what happened may affect them in terms of the competition, yet somehow he seemed to lack concern towards the one who was actually hurt in the process.
But still, Blaine understands that there was the slight possibility that nothing else could have been done, so he lets it go.
He was grateful for the amount of solos that had been handed to him, yet Mr Schuester never seemed to take no for an answer when Blaine tried to tell him to give it to one of the others who hadn't had those kinds of chances. It still happens, as Blaine is given another solo or another duet or another featured part in a group number over the others who arguably often worked significantly harder than he did. The others are still shoved aside in favour of the regulars, not even given a chance to show off what they can do.
But still, Blaine understands that maybe they shouldn't try and fix something that isn't broken, and maintain their current competition strategy for now.
The first time Blaine actually feels properly angry at Mr Schue is during 'Diva Week'. He was feeling awful, and he really couldn't have been doing with singing and dancing pointlessly for another hour before he could go home. As much as he deemed it as a defeat, he'd excused himself early from the lesson before glee club to go see the nurse so he could go home and sleep off the virus that was raging through his system before the big chemistry test he had the next day. However, he decided to stop by the choir room first to notify Mr Schuester that he was going to be missing glee practice, yet most definitely regretted this decision afterwards.
"You're early, Blaine," the teacher was sorting through sheet music when Blaine entered the room. "Shouldn't you still be in class?"
"Uh, yeah I should," he stopped to cough deeply into his elbow, his throat feeling like it was on fire. "I'll be missing glee today, Mr Schue."
"Why is that?"
"I'm really not feeling good-"
"You can't miss glee at this time of year, Blaine. Especially this close to regionals. It's only an hour longer..."
"I'm sorry but-..."
"Come on. You can't just let a little cold stop you."
He could have protested and darted out of the room against his orders, yet he didn't see the point in causing conflict. He sat back and closed his eyes, the noise from the instruments making his head ache a little more.
But still, he understands that Mr Schue's insistence that he stays in school is probably just because of how close they are to regionals.
It's the week after what was probably the most traumatising experience of his life when Blaine confirms his hatred for the teacher. He's not particularly himself after what happened; little noises make him jolt nervously, and his parents are still wary each morning as they send him off to school. It's nothing compared to how Sam's coping, darting out of the room, being Sam one minute and Evan the next. It's strange, Blaine has to admit, but he knows it's just his friend's way of coping so he plays along with him as he speaks in an English accent.
He's expecting Mr Schuester to be especially nice this week considering what happened, but he couldn't be more wrong. Okay, maybe he has to be a little stricter considering that most of the kids are acting a little out of sorts, but Blaine assumed he'd be just a little more understanding. He announces the three songs, completely dismissing the fact that not one of the glee kids seems happy about it. Marley suggests original songs, and he just outright refuses. Blaine kind of understands his reasoning- this close to regionals, it would make more sense for them to perform songs that they at least half know already as opposed to songs they'd have to learn from scratch- but he could have at least been a little sincere about it.
He doesn't care that it's sly to organize a meeting behind his back. He knows Mr Schuester is completely out of order this week, and that it's the other member's of the club taking the brunt of it, so has to do something. The songs he's chosen are all wrong, yet he refuses to completely ignore their worries about the set list. And it's not even the first time; Blaine could recall times before he'd transferred where Kurt had spent hours complaining about how he seemed to just have a stash of all of the songs from the eighties waiting to be thrust upon the poor unsuspecting glee club.
Blaine shouldn't be afraid of standing up to him next lesson, but he is. Mr Schuester is meant to be approachable, yet Blaine is already feeling a little nervous before he's even opened his mouth.
"Mr Schue, we kind of got together as a group after you gave us these songs yesterday and we came up with some alternatives-" he does his best to sound composed.
"Why would you do that?" he looks offended, and it takes everything Blaine has not to explode with the hatred he feels towards him at this moment.
"I'll go get Evan-" Sam tenses up at the conflict, darting out to hide through the use of his new coping mechanism.
"Sam, sit down!" Will shouts, glaring at him. "Honestly I don't even know what's going on in this room any more. What happened to you guys? Openly defying me?"
It's not as if he is even being stern because he's concerned about the kids; it's that he's just annoyed that it's getting in the way of his chance to win another nationals trophy.
"Unique, you need to tone it down with the whole boob thing."
Blaine shakes his head in disgust. This man is meant to be the most accepting teacher in all of Lima and maybe even America, or heck, the world, yet he thinks that this kind of behaviour is acceptable? It's awful. Just awful. The one place where she felt accepted, and even here she's being suppressed and told to not talk about it. Blaine was fine with being ostracised for going behind his back, but what he'd just seen from Mr Schuester made him feel physically sick.
"Sam, we all know you don't have a twin brother and frankly it's distracting!"
He's not even saying it because it's an unhealthy way for him to channel his problems; he's only saying it because it's getting in the way of them getting on with things.
"And Blaine? I'm disappointed in you for allowing this to go on."
He goes on to say that what they've done is unacceptable. Blaine almost laughs at the hypocrisy. And then he goes on to spout his poor little Mr Schue speech about he didn't get his cup of coffee and expects the glee kids to not be bothered by his actions, before walking straight out of the room in an inappropriate and selfish manner.
Blaine understands that Will may be acting weird because of the shooting. Blaine understands that maybe all that's going on is actually distracting. Blaine understands that Will has had to contend with drama with Finn and Emma. And Blaine fully understands why Mr Schuester is disappointed in him.
But still, he develops a hatred towards him nonetheless.
"And I'm sorry if I made any of you feel like you don't have a voice in this room," is his half-assed apology. "You do."
And Blaine's feelings are confirmed; he despises Will Schuester.