Walter is making fun of Beneatha. She is wearing African attire. She is dancing to African music when Walter comes in drunk. He thinks the whole idea of studying one's African roots and culture is ridiculous. Of course, Walter is a bitter black man. He feels that he has little hope to make it in a white's man's world.
Walter does not understand why Beneatha is so interested in learning about her African roots and culture. He and Beneatha are such opposites. He works from day to day to get by. Beneatha dreams of becoming a doctor. This is also another idea that Walter thinks is ridiculous. He insists she use common sense and become something reasonable, such as a nurse.
Clearly, Walter and Beneatha do not see eye to eye on anything. He criticizes her for caring about her African roots and culture. She criticizes him for being a dreamer. Walter desires to open a liquor store, an idea that Beneatha thinks is preposterous, especially since he drinks so much himself.