I used to work at a hardware store. Occasionally, we had a guy in who seemed very friendly; he was rather talkative. Then, he started coming in with a mannequin in a wheelchair. He dressed it up in different outfits each visit. He wasn't really bothering anyone, and he was still quite nice, but it was just bizarre to see. I actually saw him on a bike trail about 3 months after I left that job, but I don't think he recognized me.
Also, there was this one kid in band. We were coming in from some sort of exercise, and we left all of our instruments in the band room. He walks into the band, picks up a mouthpiece that isn't his and starts warming up. It takes him 30 full seconds to realize it isn't actually his, and- oh, wait, that one was me.