I remember one time when drunk at a friends family party, I convinced myself that I could speak sign language
There was this deaf kid there by himself in a wheel chair so I went over to him to cheer him up and and spinned him around in his wheel chair.

I felt really bad when I found out in the morning that he was deaf and blind and I was jamming my hands at his face for half an hour, thinking I was being a nice person. He was smiling and laughing because he knew no better, he couldn't see of hear me, not because of what I though I was doing i.e. shadow puppets with my hands to his face.
( Donkey Gums @mattcomedy, Tue 16 Jun 2009, 16:12, archived)