Quick story time: in college, it was sort of a running joke how absent-minded my roommate and I could be about locking our side door, since it was behind our fence and was essentially the back door (still dumb, but trying to give us some slack). Two of our friends came into our house while we were gone and turned all of our dining chairs upside down. I have to stress: it was conspicuous.

Roommate and I arrive home, have a conversation about how weird it is that all the chairs are upside down, and proceed to right them and go on with our evening.

The next day, the two friends who had done it held their tongues for a few minutes, until one of them said, "So...anything weird happen at y'all's last night?"

Found out they'd done it, and we'd totally undermined the joke with our total uninterest in how that could have happened.

Four years later, I still have no idea why we didn't stop to question it....