Joey Gladstone aka Uncle Joey was the resident comedian and goofball of the Full House family. Bearing a last name that would only be more appropriate for a smirking rock, Uncle Joey used this gesture when something was way too knee-slapping for him to handle. It also became his catchphrase.
Next time someone says something real funny, just tell them to Cut It Out.
Then start living in their basement and help them raise their kids.
Hand It! 