One thing I tell people is that when using sentences like "You can go to the store with Charles and I," the best thing is to test the sentence by removing "Charles and." If it still works, then it's correct.

"You can go to the store with I" is obviously incorrect. "You can go to the store with me" is correct, therefore if you add Charles to the sentence it should remain "Charles and me."

Thanks for writing this. It's sad how many people have solid ideas that get dismissed because of the poor delivery quality.