Okay, I'm not on mobile now, so I can actually type this:
For me, the breaking point for Blaine was in the S4/5 hiatus. I think I've mentioned this before, but it wasn't even so much Blaine himself as a character that precipitated this, but just the DEGREE of harrassment from his stans that led to a LOT of Kurt multishippers just completely abandoning Klaine because of fandom politics.
(Add into that, even at the time of late S4 I was of the opinion that "Maybe Kurt and Blaine could work things out, but they need to completely start from scratch, not jump into an engagement.")
... So anyway, I never watched S5b when it first aired. I'd stepped back from the show after 5x03, and was only peripherally familiar with the rest of S5 and the only S6 episode I watched before 2021 was Child Star because someone recommended the Spencer/Alistair plotline to me.
All of which is to say: DEAR GOD S5b Blaine is possibly the worst I've ever seen him.
I can come up with justifications for a lot of his S2 actions... his S3 actions except for the assault... his S4 actions aren't great, but like... Everyone on Glee cheats, it's not a specific issue with Blaine... But his S5b actions?! Jesus tapdancing Christ I hate him there.
Just the back-to-back onslaught of that Blaine & Elliott plot, then the Bash/Tested double-bill... I'm sorry, I just CANNOT forgive Blaine for Tested.
(And yes, Kurt wasn't... entirely reasonable in Tested, either... but Blaine was WAAAAY worse and in WAY more ways.)
First of all screw you and thank you for giving me the mental image of Jesus Christ tap dancing.
Seconds, I completely agree. Personally, my breaking point was between season 3 and 4. Or, well, technically season 4 had started but it came to Sweden months later so I knew Blaine cheated thanks to the internet but the season hadn't technically begun for us yet.
You're completely correct, season 5 and especially 5b is where he becomes completely unforgivable. Whilst I do hate him in every season, I think if the show had ended at the end of season 4 I could've still seen an argument for him not being that much worse than anyone else.
But in Tested he straight up ADMITS to wanting Kurt to vulnerable and dependent on him. Like he tells the audience that "Hey, I don't feel comfortable in a relationship where my partner is equal to me and I want to have all the power. Yup, that's me, I'm an abuser." How in the hell can you watch that and still be pro-Blaine afterwards??? The length to which Blaine stans will bend over backwards to justify liking him is just absolutely wild to me.
(I will also say that one of my least favourite individual Blaine moment is when Kurt breaks up with him and he says that he'll "never forgive you for this." Forgive him for what, Blaine??? Not staying in an abusive relationship???)
Also, on the note of Blaine and Klaine stans harassing people: Never in my entire life have I seen that level of harassment within any other fanbase. Like they will straight up go onto the accounts of people who don't like B/Klaine and ask why they don't like them just so they can tear their reasoning down and try to convince you to like B/Klaine. Idk man, maybe if you need to bully people into liking your faves then your faves might just suck. At this point, I'm just convinced that the reason why they harass people the way they do is because they're trying to assure themselves that they're in the right.