Depends on what effect you're aiming for.
The only clear-cut things that would annoy me would be...
POLITICALLY INCORRECT RANT INCOMING
First of all hypocrisy without self-awareness (that is, author made a very hypocritical and amoral character while the story lauds them as a flawless hero and playing the hero's "virtues" completely seriously).
And also that one weird trope where a 'gentleman' character will bend over backwards to simp over and protect every remotely pretty (adult/teenage) female character they come across like they're made of porcelain (oftentimes at the detriment of themselves and others), but then at the drop of a hat will have no qualms mistreating, hitting, molesting and 'disciplining' small children (generally males, but sometimes females as well, the second of which sends a VERY weird message about how one should treat a girl based on how old she is eg. what age does "noble, honorable discipline" suddenly turn into domestic abuse and harassment?
How curvy does she have to be for it to suddenly become sexual and bad, in the case of molestation and groping? If a woman remains flat-chested and has a small ass after adulthood, can I still hit and spank her unprovoked like you would a toddler, is it less sexual like that? What are the minimum BWH measures? What about an adult man? Is that okay?).
Anyway, stuff like that really irks me, and I've come across it WAAAY more often than I would like.
Like geez, what a noble, totally not creepy and abusive """"gentleman"""" you are, my guy. Such a role model.
Oh, and one other thing, 'calm, collected and logical MC' and 'impulsive serial killer without the slightest bit of empathy but weirdly awkward and puritanical about sexual matters for no reason' are not direct synonyms, contrary to recent popular belief on many novel sites.
It would do most authors good to keep up a bit of logical coherency, depending on the type of work. The more dramatic and tragic you make it, the more coherent it will have to be.
Aside from that, anything can work, really.
I can bet most of the things people have and are going to complain about in this thread could be perfectly fine with the right tone.
OP MC who's always right about everything? If you're aiming at an epic fantasy with classic-esque heroes, that might be annoying, yes, but if you make it a black comedy that boosts those very traits up to 11 and bases some jokes around it, you can make it very fun.
The difference between something like One Punch Man and, say, the hundredth OP so edgy MC anime is purely in the details.
And most of all, it's important to have fun. It's not like it's wrong to do all these things I just pointed out and make a fully deranged, hypocritical MC be treated like a hero. But I don't like them and personally would not want to read something with them in it.
That's all, guys. Take care.
