that can be the only reason to flag me
Unfortunately, not. In theory, the rule is, there is no rule. See the FAQ (upper right corner on Steemit.com pages):
What are the valid reasons for downvoting?
Users are allowed to downvote for any reason that they want. There are many users in the community who recommend only using the downvote on posts that are abusive. It is up to you if you want to follow this etiquette.
So in short no rules flag who and whenever you like. ☹
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