Pacta sunt servanda: please find below some initial thoughts in response to your query @Etienne.
I have just reported your last comment - hopefully aborted just in time - to be reminded of current grounds to submit a complaint. Let’s discuss each in chronological order. I have assumed that each category is deemed qualifying to sanction behaviour - otherwise their inclusion in the list would be redundant.
1: Scam or fake profile - This ground seems obvious and requires no further comment.
2: Spam or advertising - Same.
3: Hate speech - Currently defined in the explanatory note as “Promoting violence and/or making threats”. Any disguised threats should also be within scope. Borderline cases may trigger nr. 5 below (inappropriate behaviour). A strict application seems prudent in a public area where particularly minors should feel safe.
4: Adult content - Currently described in the explanatory note as “Sharing explicit or pornographic material”. In a recent forum thread a long sequence of sexual innuendos and explicit references “took over” the general thread in which minors had contributed previously. A single slip of the pen or a single implicit comment should not immediately trigger sanctions, but continuous references of such nature are unwanted in an area where the presence of minors is prevalent.
5: Inappropriate behaviour - Currently labeled as “Persistent, intrusive messages despite explicit refusal”. This capita selecta category may include a variety of posts. You have mentioned above that people should refrain from insulting each other. Should this be interpreted as including both “grave insults” and “incessant insults”? This would seem reasonable to me. Not each single insult should warrant intervention. The severity and/or the repetitive nature may be a different story. See below on interpretation issues. Your idea regarding dark humor and provocative jokes seems to make sense. Generally permissible, but should refrain from e.g. disguised hate speech or have a repetitive nature to push a certain substantive agenda.
The above comments have been made with the protection of minors in mind. Considering that the forum feature is public, a less stringent set of rules concerning adults is redundant unless the site will cater for a secluded area for adults to exchange forum posts.
Also be mindful that social media age limitations are being or have been introduced in various countries across the globe. Many of such limitations are of a mandatory nature and non-compliance may invite sanctions to be applied.
As most cases mentioned above will be context driven and subject to interpretation of generic rules, the exercise of discretionary powers of moderators will often be decisive. To make intervention more palatable, I suggest to include an “Official Warning” as a means to intervene in borderline cases. A temporary or permanent ban may be imposed if the Official Warning is ignored. Upon an account being banned in severe cases - such as hate speech - I suggest to automatically delete all content of such user. No need to keep forum visitors exposed to content which triggered the ban.
Please note that the above already largely applies considering current grounds to file a report. Some further clarifications have been attempted when interpreting current rules.
Too complex for some? Not a problem as long as they follow common sense. When going out of bounds, an Official Warning may cushion the intervention before a ban of any nature is imposed.
I have conveniently ignored any outer limits imposed by law. The main concern should be the exercise of discretion considering the current demographic of this penpal site.
Happy to discuss further and open invitation for others to contribute - preferably in a constructive and respectable manner.