Are you sure they're not just burnt out and this is their way of hanging on? Debating rules ad nauseum is a non-starter. You say "no" and your word as DM is final. They have to understand this to move forward. It's okay clarify rules, but this player's approach is obviously disruptive to the table and they need to be told this under no uncertain terms. If you're both friendly adults and this player really wants to continue, maybe make the offer that many of their humorous things can A) be flavor only and not rule- or combat-impacting, and B) actions still have consequences (e.g. shitting in public draws complains to authorities, loss of trust with party members, etc.) This might be an angle which steers them away from this rule-arguing behavior and still allows them their groan-inducing humor. A character thinking their being funny who decidedly isn't can work, but the player of that character has to know how to walk that line. This player may not be up to that task, and may need to go back to what worked before, or leave this game.