a polite way for saying "leave" or "get out" in Korean, it is also an exo inside joke that exo-l's use all the time.
Person: Do you like Seungri
EXO-L: ......nagajuseyo
nagajuseyo is a korean world means ' get out please' it got known between kpop fans when EXO's member Zhang Yixin aka Lay said it to Baekhyun to leave the dancing room for him to practice.
Raya: can I touch your buttcheeks?
Taeha: Nagajuseyo.