The next day of school, compensating for weekends, breaks, vacations, snow days, teacher work days, meteor days, and the like.
"Oh shit, that paper's due tomorrow!"
"Hahaha, there's no school tomorrow, FAG. Tomorrow's Saturday!"
"Err.. uh.. I said schoolmorrow. Yep. Schoolmorrow."
"Hahaha, you don't know what schoolmorrow is? FAG."