So yeah... I took my first sign language class last year during the summer. There were several really funny things that went on, but one of them was when Carrie, our professor, tried to show us how to say "good to meet you". I went to repeat it the next class and I signed "meet" only horizontally. >_< Apparently it means to do the mattress tango. She explained that to me in front of the class and I swear my face was sooooo red....
There was also another situation where one of the other students who worked with several students at various intervals of the autism spectrum, was trying to remember a sign that the boy tended to use a lot. He already knew bathroom, and mom, dad, that sort of thing, but what he was signing was "water", like thirsty. She signed a "B" against her chin. Carrie waved her hands frantically shaking her head and laughing. She shut the door and explained to us that here at least it means "bitch".
Omfg. I had to really leave my pride at the door when it came to that first semester at least. There were so many funny mistakes.