Was going away for Christmas. Just got chucked off my flight because I refused to put away my model helicopter.
However - for years as a kid I would try to knock myself out by standing in the bit of the railway carriage nearest the door. I would stand facing the direction of travel, about an inch away from the bulkhead. Once the train got up to speed, I would jump off the floor to see if the train would knock me out.
It worked.
But only because I jumped so hard I collided with the ceiling........
and I always thought that "relativity" was a Christmas play starring my cousins.