The showbiz art of upstaging someone. It began when it was Sammy Davis, Jr.'s turn to move down on Johnny Carson's couch to make room for the next guest. WHen that guest said something funny, Sammy would react by laughing loudly, slapping his knee and falling to the floor. The audience would then begin laughing at Sammy and not the guest.
When one has been served "a glass of Sammy" they have beensilenced for their wrong doing. It is not a rude word or meant as a insult. The name Sammy stands for justice for those who annoy others.