2 things that I've had to convince people that are real:
1. Once I was describing to someone about water dowsing. This person didn't believe that it was real and that it was folk lore/myth. Of course it is real....water dowsing is used all of the time. The oil industry have even use dowsing rods to locate water courses in preliminary survey's prior to sending hardware into areas for further investigation, for years.
2. Narwhals. I had to actually go onto google images to get a picture up. To be fair to them they were probably getting confused with Unicorns or something.