This thread reminds me somehow of the Robert Burns quote:

O wad some power the giftie gie us
To see oursel's as ithers see us!
It wad frae monie a blunder free us.
And foolish notion;
What airs in dress and gait wad lea'e us,
And ev'n devotion!
In more modern English, it says "Oh, would some Power the gift give us
to see ourselves as others see us!" and I'm sure you can all suss out the meaning of the rest.

I learned by first grade that one would not make friends by correcting one's classmates' grammar - but I did so anyway when it really bugged me, especially my neighbor who pronounced spaghetti as "puzgeddy" ...

My pet peeve are misplaced apostrophes, and when I see them used incorrectly on signage or in an advertisement, I will tell the store employees, especially on handwritten - and therefore easily corrected - signs.