It's probably a combination of your typing style and your opinions that send red flags. /a/ shuns a lot of buzzwords and memes that are commonly used on other boards.
Any of the following things will almost certainly get you marked as an outsider:
>kek
>cuck
>ebin/epic
>moeshit
>:^) and any other "ironic" emotes, with the exception of ;_;
>"meme" as an adjective or descriptive noun
>talking about feminism
>talking about gamergate
>talking about politics outside Japan
There's also several opinions that are associated with anime casuals and outsiders, like
>modern anime is all garbage
>the industry is dominated by moeshit
>the industry is dominated by haremshit
Etc. These are things that annoy the majority of /a/nons because a) none of them are true and b) they are expressed in such a lazy, entitled way.
That last part touches on one of the most important things about /a/: if you're not heavily invested in watching anime, your opinion counts for very little on that board. They have no time for casuals who've seen fewer than 50 series acting like they know how the industry works and what's wrong with "modern anime," and opining on genres they've never watched and don't even understand the appeal of.
TL;DR for this post: if you don't actually watch a shit load of anime, shut the fuck up and keep your head down. Post as little as possible, only post about things you actually understand, and avoid using memes and buzzwords. People WILL call you out when you spout bullshit.
