I missed the obvious fact that, when I was going to program a game for my high-school final year project that started as an in-joke with my friends, I should have gotten the face of one of my teachers in there with a South-Park style opened mouth removed before I took a screenshot of it and showed that to my consultor for the project to have him approve my idea. I didn't actually realize it was really stupid of me to leave that in until I showed my consultor, who obviously recognized the other teacher's face straight away. It took around ten minutes before I noticed he was looking at the pictures a lot and finally realized what my mistake had been. I then explained to him that it was an in-joke with my friends and then foolishly continued explaining the in-joke, which made it just that much worse.
His response after all of this?
"Let's just keep this between the two of us."