When I was little there was a girl who did. The lights in the girls bathroom were always off (sometimes I would turn them off myself but shhhh! don't tell anyone) she believed in Bloody Marry so she was super scared to go in the bathroom. Some girls dared her to go in and they closed the door while she was inside and the lights were off. When the janitor came, she was on the floor crying and trembling...I think they said she peed in her pants :(
I've never done it, but I don't believe in it.
No, no, I really don't.
No, but if you say "Biggie Smalls" in front of the mirror on All Hallows Eve, the former rapper will emerge and try to shoot ya.
I believe in a lot of things, but I think if Bloody Mary did exist, authorities would've either banned mirrors/called the Winchesters.