Tricking Nerdy Step-Sister Into Face Sitting

My plan is to stay home reading a book alone on Halloween but my cool older step-brother surprises me with a costume and an invitation to a party! I am a little nervous but he convinces me to try on the slutty school girl uniform and even to wear it with no panties on under the tiny skirt. Once I am dressed up to go out big step-brother tells me that he just needs to check one last thing under my skirt before we leave. I guess I don't know much about parties because I am not sure why he needed to check both my holes... with his tongue!