Most Helpful Guy
That is sometimes how men react to each other other and they don't mean anything by it, I guess you could call it a term of endearment when they are frustrated because they know you are right, but don't really want to admit it. Sometime a guy might be comfortable enough to do that with a girl. So you could take it as you guys are really good friends and he's comfortable with saying that to you, not always the case but a possibility. I don't know since that is between you guys. On a side note a good comeback might be "In your dreams". Anyway the only way to know truly is to ask him and discuss it a bit.