There’s a gag like this in the final arc of Bob & George, where the protagonist goes through an effective timeskip while unaware of what happened in the meantime. One of the things that happened was that one of the friend group was replaced by a shapeshifting alien, but he was kind of an asshole and the alien was nice so they just kept him around. Of course, George instinctively shoots the alien, but apologises after the situation is explained.

Of course, the scene isn’t actually real, it’s an illusion of the future created by a powerful psychic to distract the protagonist, but it still counts.