1. I was recently reminded about the claim that "I and you" or "me and you" are grammatically incorrect -- not because "I" is being used instead of "me" or vice versa, but because it's wrong for "I" and "me" to go first. (Here's one sample I just found online, but I've seen others.) But that, it seems to me, is a principle of politeness -- let the other person go first -- and not of grammar.
2. Relatedly, the recent reference to Cohen v. California -- the case that held the government couldn't punish the wearing of a jacket that said "Fuck the Draft" -- reminded me of this passage from Justice Harlan's opinion:
First, the principle contended for by the State seems inherently boundless. How is one to distinguish this from any other offensive word? Surely the State has no right to cleanse public debate to the point where it is grammatically palatable to the most squeamish among us.
But there's nothing grammatically unpalatable to people about such vulgarities. "Fuck the Draft" is perfectly grammatical. "Fuckingly the Draft," I suppose, wouldn't be, but for that very reason I doubt that even lovers of vulgarity would wear such a jacket, unless they're trying for some linguistic absurdism.
3. So my question: Are these unrelated errors, or is there some reason why people sometimes refer to certain usage rules to grammatical rules, when the rules are actually rules of good manners?