Flagging is an in-built moderation measure in Discourse, intended to dissuade bad behavior and spam, as well as to promote civilised discourse. If you want to raise an issue about a post without derailing the topic at hand, the best course of action is usually to flag it.
Thought it was worth pointing out that Discourse has a system designed to prevent threads being derailed by off-topic reactions to posts
Arguments easily spiral online – this shouldn’t be news to anyone…
In order to keep conversations on track it’s best practice to flag them for a moderator to review, rather than escalate the situation publicly by reacting
You can find the flag via the “…” at the bottom of any post. Click it to reveal the window below
You also have the choice to send the Discourse user a personal message – use this channel with care and politeness to encourage a member to reflect on something they have posted. This is very useful if you’re on good terms with the user to support them, and avoid a flag and moderation
More reading at meta.discourse
If you would like to be a moderator (it’s usually very little work) and help to keep our online forum friendly and safe please contact the @directors