This grammar is totally used in a non-formal situation, especially speaking to your friends or families or someone who is close to you. In the conversation you posted, I guess this person B doesn't normally get up so early, so person A said this sentence"干嘛啊你" instead of "你干嘛啊" to express some kind of surprise. In some kind of short sentence, in order to express some feeling like surprise or sarcasm(in a joke way), we normally put subject at the end of sentence.