“Zo gek als een deur”
To be as crazy as a door. A normal Dutch saying to most, but if you think about it, it’s the saying itself that is actually crazy. No, “deur” doesn’t actually mean door here. Hundreds of years ago ‘dore’ was a Dutch word meaning fool, so the saying would have been ‘to be as crazy as a fool’. That makes a lot more sense! Most Dutch folks aren’t aware of this, so this truly is inside information.