What if your boss...?

what if your boss, out of nowhere seemingly, confronted you in the middle of the store you worked at (there are two buildings, and this wasn't the main room, but still would be out in the open nonetheless) and, not in a hushed voice either, accused you of systematically undermining their authority after a misunderstanding on their part, and you were told that you were going to be written up and if anything similar happened again, would be dismissed. it should be noted that what you would do should be based on the boss genuinely being wrong in almost every way, but typically being a good person/boss otherwise. am i wrong in thiking this is way, way over the line? what would your reaction be, especially if only a few months remained on the job anyway....?