I was recently at a wedding where one of the guests at my table (people from the other side of the new family) said something about the "maid of honors". Another person sitting next to him quickly leapt in to correct him into saying the "maids of honor," and I was then witness to a ten-minute, heated argument about whether or not it mattered.
So that is my question to you, philosophers. How much does it matter whether a person makes minor grammatical mistakes, so long as everybody understands what is meant? How important is it to say "My friend and I" instead of "Me and my friend," or "Passers-by" instead of "Passer-bys"? What is at stake?