Oh boy, this reminds me of one test in college where there was a question that had a logical circuit diagram, I don't remember what it asked exactly but my answer was marked wrong, I went to the teacher the next day and told him I thought that was the right answer and he said "well, it's not, I'll demonstrate" and he wrote the question on the board called attention for everyone saying he would show the right answer to the test question, and started answering it. I saw him start to answer and immediately he made a mistake, I raised my hand to point that out and he told me to let him finish. He got to the end of the thing, showed a different result, and said "see, this was the correct result" to which I said "You missed the NOT at the beginning of the circuit", he looks at it, rewrites some stuff, and gets to my answer to which I said "and that's what you marked as the wrong result on my test". He still tried to claim that was wrong because he got the question from book X, and a colleague (who I suspect had also given the right answer) produced the book, looked up the answer and said loudly "the second answer is the one on the book". Defeated he had to give me (and whoever else had the right answer) at the point for that question. Completely unrelated story, that guy was also the coordinator of the course I was coursing and after months of waiting for recognition of some classes that I had taken at a different college coincidentally the very next week they got denied which meant I would have to take 14 extra classes (so at least a year and a half extra) to graduate, and that some of the classes I was taking that semester would have to be dropped and retaken after coursing the prerequisites (which I was trying to get recognized), one such class was the one where I got the question right... What a coincidence, right?

I should thank that guy, because of him I dropped out of college, moved to another city, and started at another college where I met my wife.