Painfully stupid
When someone is so dumb it’s like watching a train crash into a giant pile of spaghetti and everyone else around them gets hit with the explosion of stupidity.
My cousin thinks the Earth is flat and that the sun is just a giant light bulb.
My brother tried to explain the plot of Titanic and said it was about ‘a boat and a guy who cried.’
My dad thinks the moon is a giant cheese wheel and still doesn’t get why it’s not edible.