Q: My boss corrected me for writing “with John and me” in a memo. He insisted that I should have said “with John and I.” I didn’t want to get into an argument, but he was wrong, wasn’t he?
A: Yes, you were right. Mistakenly using “I” for “me” is probably the most common grammatical error in English. Nobody makes a mistake when “I” or “me” is used alone. No one (at least no grown-up) says “with I” or “me went.” So if you can’t choose between “I” and “me,” it helps to mentally eliminate the other guy: “with [John or] me” or “[John and] I went.” You can find more hints about solving “I” vs. “me” problems in the first chapter of Woe Is I.