Let's take a look at the Korean sentence pattern Noun + 야말로. We use this to throw a question or remark back to someone because we think we should be the one saying it. For example, I was working on my painting in the art room when someone came in and hurriedly hid herself at the back of the door. She didn't notice me. Curious, I stood up to check who she was. It was Hyemi, a classmate of mine. The moment she saw me, she asked What are you doing here? (여기서 뭐 해?) But that was my question too. I should be the one asking it since I was an art club member. There was no reason for her to be there. So I use 야말로 to throw the question back to her. We were the same age, so I used (you) to address her in second person. 야말로 is attached to the name or title of a person before repeating the question or remark. The actual sentence is 너야말로 여기서 뭐 해? If the name or title ends in a consonant, use 이야말로 as in 형이야말로.

너야말로 연애 좀 해라.

Mind your own love life. Don't tell me to date anyone because you are single too.

오빠야말로 청소나 해!

How dare you to tell me to clean. I've never seen you clean the house either. (talking to oppa)

형이야말로 여기 왜 왔어?

Hyung, what brings you here? (I am more surprised that you are here)