야 인마! means ‘hey, dude or homie.’
인마 is from 이놈아 when older men call out younger men.
야 basically means hey. You don’t use this to anyone older than you. You can use this to someone at the same age or younger than you are. You can use this when you are angry. It doesn’t always express anger. It is merely used to call out someone or to direct their attention to you.
인마 can be translated as man, dude or homie. Often older people use this to younger people or their kids. Men also use to one another. Women don’t tend to use this. This is not profanity, bur you don’t use this to strangers.
야 and 인마 are often used together.
야 인마, 여기서 뭐해?
인마, 이렇게 하면 안 돼!
인마, 왜 늦었어?