This is a thought which occured to me in church the other day when I suddenly folded my arms and refused to continue listening, singing, etc. because I had seen an error in the news sheet. "But it's wrong and it looks horrible," is what I would scream (or whisper urgently to the friend sitting next to me). Let's look at what sin is, what grammar naziism is, and whether I should repent of it. Somehow, I don't think I'm going to like the conclusion.
I would define sin as anything which prevents someone from having a relationship with God. If I do something of which I am ashamed, this prevents me from coming to God, being honest with him and opening up to him.
I would define my grammatical condition as such that I cannot not spot errors in punctuation, spelling and bad wording. When I spot a grammatical error, I freeze. It makes me unsympathetic, grumpy and often rude. It also makes me look down on those poor illiterate people who have written whatever it is that has offended my eyes. Do I ever wish I didn't spot these errors? Not really, because I like things to be right. If something isn't correct there has to be a reason for it, for example for comic effect.
If being so fussy about grammatical correctness is going to make me freeze in church and stop worshipping, praying or listening, then surely it must be a sin. Being unsympathetic, grumpy and rude are traits also associated with sinful nature. I fear I must conclude that my grammar-fussiness is sinful because it is stopping me spending quality time with God and with others in church and is creating in me an attitude of superiority and pride, yet more characteristics which are condemned in the Bible.
It isn't going to be easy. I'm going to have to make a big effort to not let the proofreader in me get in the way of the worshipper. I don't think I'll ever not love perfect punctuation and flow-off-the-tongue (or pen), complex sentences [Douglas Adams] with beautifully rich vocabulary [Stephen Fry], but if I can stop it getting in the way of worshipping and instead use it for good, surely that is the best thing to do.