When proper usage impedes communication

This question may be moderated as unanswerable, but I am interested in opinions.

Take this scenario: Most people I know will improperly correct "The ball belongs to John and me." to "The ball belongs to John and I." The simple rule I was taught is that you remove the other party and see if the sentence makes sense. Would you say "The ball belongs to I?" No. "The ball belongs to me." Therefore, the correct wording is "The ball belongs to John and me."

If I am giving a talk to a group of people and use the correct "John and me" construct, I will cause a good portion of my audience to lose focus as they mentally (improperly) correct my grammar.

My question is this: If the purpose of language is communication, what do you do when proper grammar is a barrier to effective communication?

Do you use the proper construct, causing over half the room to stop paying attention; do you use the improper construct that most accept and lose the respect of the more educated people in the room; or do you avoid the situation altogether by wording your thoughts such that you don't need to use the distracting construct at all?

You should use whatever language is best to communicate with your intended audience, whilst still keeping to standards you're comfortable with.

• If it's a formal setting, use formal language.
• If you're talking in the pub, you can use slang.
• If the audience are domain experts, use some technical and jargon words.
• If you're meeting the queen, use super-formal language.

Now, I wouldn't recommend talking in street slang with gang members as this probably would be incongruous, but you would still tailor your speech to be understood.

If saying "and I" is going to cause such a huge barrier to understanding, by all means avoid it. But I have trouble believing that both (a) most people would use the incorrect form, and (b) it would cause over half the room to stop paying attention.

If that's really the case, then for your sanity, for the respect of the more educated people and to avoid losing the majority, use some other wording instead.

The case in point is 'proper usage'. As the authors of 'The Cambridge Grammar of the English Language' write, persuasively if controversially, I in coordination with a noun or another pronoun in object position:

'. . . is used by many highly educated people with social prestige in the community; it should be regarded as a variant Standard English form.

They add in a 'Prescriptive grammar note':

Those who condemn it simply assume that the case of a pronoun in a coordination must be the same as when it stands alone. Actual usage is in conflict with this assumption.

On the broader point, language is used for communication, but it does other things as well. It helps us tell the world a little bit about ourselves, for example, and in a dialogue it establishes and reflects the power relationship between the participants. It is misleading to speak of 'proper grammar' because, to express the point in admittedly extreme terms, every utterance is grammatical one way or another, if we exclude slips of the tongue and finger. Whatever dialect we speak, we speak it according to grammatically consistent rules. That is not to say we shouldn't try to match our language to the situation in which we are using it, very much as Hugo suggests. In many cases, that variety will be Standard English and, to get there in the end, it is the use of Standard English that I suspect the OP has in mind. That means saying things like I don't have any rather than I ain't got none and He did it well rather than He done it well. The take-home message, however, is that those non-standard forms are just as grammatical as the standard ones.