심보 is similar to 마음 as in talking about someone's attitude, personality, or in general mind or heart, but it's generally used for something negative. "무슨 심보야?" can be translated like, "What kind of person are you/is he?". And it would be used to comment on someone's bad behavior or to note attitude problems. Other example sentences: 심보가 고약하다 (He/she is ill-hearted.) 너는 왜 그렇게 심보가 못됐니? (Why are you so mean?) Hope that helped!