A matchmaking rule to prevent matching against a specific blacklist of other players.
This would be used whenever a user has blocked some other user because they do not get along (abusive behavior, personality mismatch etc.).
Re-entering matchmaking if a blacklisted match is returned is not an option, as there is no guarantee that this will ever terminate.
The current set of rules does allow this. The only rule that looks similar to what we need, is the set intersection rule. However, set intersection matches if there is an intersection above a certain size threshold. To make this rule work, we would need to invert the limit, i.e. requiring that there to be no overlap at all, and match the set in the current ticket against the set of members in the other tickets (rather than the same set in other tickets).