This has been urban legend for the longest time.
No definite proof.
It's funny. I think that this is one of those things that is so entirely difficult for the average person to grasp because the thought of it is so deplorable, that if any actual definite proof was produced, people would just continue to rationalize how ridiculous it is.
I think that is why it is so often easy to hide things in plain sight before the masses and also paint someone as crazy.
You can have a bonafide real experience right now that would be characterized as incredible and unbelievable, but you, yourself, experienced it - soberly - and when you try to relay the details of your experience to someone else, even someone you trust, if it sounds unbelievable, their first mind is going to be to ask you if you are ok, if you are on something, if you are joking or anything other than accepting what you say is true.
I don't know if it is people having a vested interest in accepting reality exactly as it is presented to us in order to maintain their own sanity or what. It is not too hard to believe some of this stuff as true though.