Because teachers, no matter how kind, no matter how friendly, are sadistic and evil to the core.
Don't you find any irony in a vampire sucking up?
The world is full of monsters with friendly faces.
Dude, you're a vampire. EVERY day sucks for you.
A crease found it's way onto Joss's forehead. Because he was certain that Sirus was wrong. Girls were more complicated than boys. Girls communicated in a language that only they understood. And Joss wasn't sure at all that he would ever understand them.
Lesson #456 of high school life: Never, EVER trust an alarm clock.