Miss Ritter

I had a professor once who liked to tell his students there were only ten different plots in all of fiction. Well, I'm here to tell you he was wrong. There is only one "Who am I"?

— Mr. Parker? Tardy again. Well, at least we can always count on you.
— Sorry, won't happen again, I promise.
— Don't make promises you can't keep, Mr. Parker.
— Yeah, but those are the best kind.