Man this is kind of sort of following the plan I said he should do: Pretend to be weak and meek, aquiesce to him to make him arrogant and bolder, goad him into pushing you in ways the law does not support (but is fine when no one reports), then stand your ground and have him try to bull you over, corrner him by not budging and making it a known incident and force him into a duel, kill him.
MC doesn't want military action because of the inherent deaths, so a one-on-one duel is pretty much the best thing he could get. It reminds me of the story of a notable viking that bullied some others by challenging them to duels as a part of legal disputes, which he was sure to win. Think it ended with him dying to a greater opponent when he challenged someone and the hero stepped in (and he couldn't withdraw it without seeming a coward).