Why does boy willie tease doaker about his profession?

Boy Willie teases Doaker about his profession as a railroad worker to highlight the differences in their aspirations and lifestyles. He views Doaker's steady job as a symbol of complacency and contrasts it with his own ambitious dreams of selling the piano. This teasing reflects Boy Willie's desire to break free from traditional roles and pursue what he believes is a more meaningful path, emphasizing the generational tensions and differing values within their family.