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."