Here’s a sample official warning for you to use. I’ve added the theory that this person is trying to abuse an automated flag-handling system to get the victim’s account automatically penalized, and refuted it.
Hello, I’m contacting you again about your continued use of flags on posts you merely disagree with.
Your behavior is causing a lot of extra work for the forum moderators. This isn’t like Facebook or Twitter where you can score a win by convincing the automated flag system that something’s wrong with the account you are flagging - we are looking at these bad flags and rejecting them ourselves.
If you persist in abusing the flag system like this, you will receive a 7 day suspension from the forum.