I'm a bit of a grammar police. But in moderation. I won't fuss at you for ending a sentence with a proposition. I think "to whom" is the funniest sounding phrase. I also won't blame you for saying you're good instead of well.
But if you confuse "then" and "than", or "lose" and "loose", or say "had went" instead of "had gone", I'll try not to correct you in public. I really will. But I'll be cringing on the inside.
And in writing, mix ups with your/you're and there/they're/their will make me cringe. The expression "could of" instead of "could have" just makes me sad.
And I really hate it when people forget to use their commas.
I understand that it is now perfectly correct to leave out the oxford comma and say "I need milk, eggs and bread." But I think it looks ridiculous. I mean, just do a search on Pinterest or Google Images to see the flaws in this new grammar rule. (side note: some examples aren't very appropriate.)
I'm sure in twenty years, people who use the oxford comma will be comparable to those who still put two spaces between sentences. But I'm sure I'll still be doing it. That's what looks right to me.