He thinks the sun is a planet; he's not playing with a full deck.
he's not playing with a full deck
idiomHe's dumb
Origin
disputed origin20th-century American slang: a card game played with cards missing can't be played properly.
After he tried to wash his laptop with soap and water, everyone realized he's not playing with a full deck.
The neighbors often whisper that the old man is not playing with a full deck because he spends every afternoon trying to teach his cat how to speak French.
Last updated June 7, 2026