Pinochle player

Another way of saying someone isn't playing with a full deck, aka someone who's not too bright. The phrase comes from the fact that pinochle is played with only 48 cards in a standard 52 card deck. Therefore, while playing pinochle, one is literally not playing with a full deck.

"You know how Jason had to take a DNA test to see if he's the father of Cassandra's baby? Well, he asked why she didn;t have to take a DNA test to see if she was the mother. My god, what a pinochle player."