My best friend does the knock on wood thing. Could never tell if he was joking or actually believed in it. Would be over such small things. We'd be playing a game and he'd be all "holy crap, we're gonna win....knock on wood". Black cats? Hard to imagine anyone believes in that. Mirrors? Well, I'd say it's bad to break one because they cost money =P Or the number 13. I haven't been to a building with 13+ floors so I don't know. Haven't been to an airport in a decade so no idea there either. Anyone here have an odd superstition?