When you call a spade a spade, you tell the truth about the matter. Even if it means being unpleasant. In other words, you tell it like it is. You are very direct, no matter how unpleasant or embarrassing. You speak plainly and frankly.
Example: “My uncle always calls a spade a spade. When I was young, whenever he found me saying or doing something stupid, he didn’t hesitate to call me an idiot”.