Does this mean that my step brother has no respect for me?

he thinks that because you're a girl first of all, and because you're younger than him second of all, that you are responsible for cleaning up his mess. you are not his maid, or his woman. let this be known to him. tell him that outright. and also please speak to your dad and step mom about his infantile behavior and disgusting mess. insist that you two not share a bathroom.