Literally "You're already dead" in japanese. A phrase used by the character "Kenshiro" in the manga/anime "Fist of The North Star", also know as "Hokuto no Ken" in Japan. This phrase is very well known by the the otakus/weebs(anime/manga fans) because is very common that a otaku/weeb watch the original dub of an anime.
Ha! Omae wa mou shindeiru.