I Need to Rant

Why can't people respect other people's time? I am online English teacher and I really hate students (especially their parents) who think they can have or cancel class last minute. It really irritates me when they act primadonna. Like they can come and go. Don't they realize that I could do something with the time that they are making me wait. I am not paid for the waiting time. I am not a slave that you call whenever you freaking need. You have to notify me hours before the actual class, so that I can prepare for the class. Argggg!!!