Recently I've come to realize that I mentally talk to the author/writer when reading a manga or watching an anime. For example, when something overly coincidental happens I might think "C'mon, couldn't you have thought of something better?" or "Fuck you!" when one of my favourite characters is killed off. Anybody else do this, or am I just weird?
Most recently, I've been reading Kimi no Iru Machi, and I've been begging Seo-san (author) not to replace Eba with Asuna as the love interest of focus. Once per story please, and not with brand new characters!
As a writer, I can't help but always wonder what the author was thinking or how they were able to come up with their dialog/premise/plot or whatever.
The only time I get upset at what I read is when I can tell the story wasn't thought out. If it seems like the author kills someone just for shock value, or they make a good guy a bad guy or vis versa for no reason then just to surprise you, I'll be upset.
Even if I don't like what the author did, I wont be to mad if it at least makes a bit of sense why they wrote the story the way they did.
I don't usually question something that an author does but I always wonder if he knows how changing something will affect the story or if he will just make it up as he goes along.