Ghosts don't exist, mediums and psychics are charlatans preying on the gullible, the Ouija board is just a game, and there's no life after death.
Waterboatman "There's plenty of evidence" - er, no there isn't.
Whenever somebody says they've seen a ghost or experienced something and somebody who deosn't beleive questions it, the default position seems to be "are you calling me a liar?". I wouldn't say people who claim to have seen ghosts are lying, but I would say they are mistaken. They seem to take umbrage that somebody doesn't beleive they've seen a ghost - are we meant to suddenly change our mind just because somebody claims they have seen a ghost? I wouldn't expect them to beleive me if I told them I'd seen a leprachaun.
Surely by now we'd have some evidence of ghosts (pretty much everybody has a camera on their phone now), particuarly given the billions of people who have died over the centuries.
A few other things that are complete nonsense with no evidence to back them up...
God.
Fairies at the bottom of the garden.
ESP.
Homeopathy (massive massive con trick).