The words bellow are not formal word, used orally.
二百五, noun, literally it means quantifier 250, but when it describes someone, it says someone is idiot, foolish, moron. For example: 这人就是个二百五。Sometime, people only say 二 shortly, it's similar to 二百五, but it's an adjective. For example: 这人很二。
缺心眼, it's not lacking of heart point. In fact, the true meaning is someone stupid. For example, 这人缺心眼。
少根筋, it means stupid too, not lacks of muscle. For example: 他少根筋。