The issue is that triggering a flag implies a strong reaction to something that has some level of gravity.
Sometimes people do actions that are inappropriate but not grave, and sometimes they do it because they do not see the implications (lack of online social skills), or do not understand the technical scope, and it bothers the conversation.
Triggering a flag on such a post can be received as aggressive and be perceived as a tentative to denounce the content of the post itself (particularly if the conversation is a little tense). There should be a way to say please moderator make sure this user respects a better behavior, without making to much of a strong intervention in the conversation.