그래 can be a contraction of two phrases: 1) 그러해, 2) 그리해 or 그렇게 해. 1) 그러해 (adj) = 그러하다 + 여 -> 그러하여 -> 그러해 = be like that; be in that state. 2) 그리해 (verb) = 그리하다 + 여 -> 그리하여 -> 그리해 = do/act (like) that. (그리하다 has the same meaning as 그렇게 하다 which is most common in modern Kroean) So 왜 그래? can means "Why are you doing that?" or "Why are you like that?". You can say that to someone acting strangely or who is in a nunusual condition like being upset, sick, etc. 왜 나한테 그래? is usually a reaction to someone who is complaining to you about something you're not responsible for, like "Why are you blaming me?", "Why are you taking it out on me?", etc.