Five open carriers went into a restaurant. One patron called police to check them out, stating she "felt uneasy" despite their calm behavior. The city is classifying it as disorderly conduct (disturbing the peace), noting "The DC statute does not require an actual disturbance take place, only that conduct in question is of a type that tends to cause or provoke a disturbance."
The relevance of that is unknown. The city's position must boil down to — conduct that is both legal and peaceful becomes a misdemeanor if it upsets someone to where they call police. And that, even if it is constitutionally protected. It seems like a 2A version of the 1A "hecklers' veto" — we will ban your speech, the content of which is permissible, because your opponents might become violent if you gave it.
UPDATE: the point about respondeat superior raises an interesting issue. In a §1983 civil rights action, there is no respondeat superior liability (as I recall, because a violation of constitutional rights cannot be within the scope of duty of a government employee). To make a governmental unit liable, you have to prove that its organizational actions were wrong — one approach being to argue that the unit gave insufficient training to its agents. Usually, though, this is more easily claimed, than proven.
But the City has just officially determined, as an entity, that disorderly conduct charges should be issued. It's no longer a decision by officers on the scene, but an official determination by the City through its highest decisionmakers. I think the City is on the hook.