Another incredibly elaborate prank, this one from Germany. It involves a washroom with a mirror that is in fact transparent glass, with an identical, mirror-image washroom on the other side. A pair of identical twins who move in unison as in the classic mirror scene from Duck Soup, completes the illusion.
Incidentally, this hand washing area appears to be unisex, with a sign directing Damen und Herren to their respective rooms for more serious matters.
When a victim of the prank starts to wash his or her hands there's a moment of dawning realization that he or she isn't casting a reflection. When the woman cheerfully suggests to one victim that he might be a vampire, he seems a momentarily little troubled by the suggestion, but not very much. In fact, what's interesting is that nobody seems especially upset by lacking a reflection, just mildly surprised and curious. For the most part they engage in some sensible experimentation, for example standing behind the woman to see if only one side of der Spiegel ist mucked up.
Incidentally, not too long ago I had a similar experience. I was in a Chinese restaurant near my home, and as I was getting up to leave I happened to notice that there was a large hexagonal mirror on the wall. When I walked past it I expected to see my reflection, but I didn't. It took me a few seconds to realize that what I was looking at wasn't a mirror but a framed hexagonal opening in the wall between two parts of the restaurant. I figured it out quickly enough that I didn't have time to start fantasizing about Buffy, but for a moment it was a curious experience.
At other restaurants I have experienced being apparently invisible to the wait staff, but that's another matter.