What is the ruling on saying: "May his good be cursed?" What does it mean? And does it reach the level of disbelief?

Linguistically and technically, "لعن" (詛咒) means expulsion and banishment from Allah's mercy. The phrase "يلعن خيره" (may its goodness be cursed) is used by common people to express astonishment or to indicate the severity of harm, without intending the actual meaning of cursing. However, one should avoid such expressions so that a Muslim does not become a frequent curser, and because the word carries its linguistic and legal connotations. Islamic law has forbidden cursing animals and inanimate objects, and a curse, if it finds no justification, returns to its utterer. The saying "يلعن خيره" does not necessitate the disbelief of the speaker or the one whose goodness is cursed.