This phrase is not necessarily a slang, but a popular Spanish saying that means 'A thief judges by his condition'. It refers to the idea that people often project their own faults onto others because they assume others are like them.
Examples
- Spanish: No confía en nadie porque siempre piensa que van a engañarlo. Como dice el refrán, 'el ladrón juzga por su condición'.
- English: He doesn't trust anyone because he always thinks they are going to cheat him. As the saying goes, 'the thief judges by his condition'.