English Translation
Complete nonsense!
말 (mal): This means "word" or "speech" in Korean.
도 (do): This particle is often used to indicate emphasis or comparison.
안 (an): This means "not" or "un-" in Korean.
되다 (doeda): This means "to become" or "to be" in Korean.
Together, the expression “말도 안돼!” can be translated as “It’s not even believable!” or “It’s unbelievable!”