Not sure if note-passing is still necessary in the era of smartphones. But back in my day (*adjusts old lady glasses*), it was all the rage and a great way to make class go by faster, entertain your friends, and make yourself Public Enemy #1 with your teachers. Note-passing was equal parts exciting and terrifying, because if a teacher intercepted it, you were at risk of a scolding, detention, or worse, being publicly shamed by them reading the note out oud.
1.) From ccjrod:
I found a note under the seat of an extremely talkative female student after class. I knew she was dating a student called, "Ron." It listed all of the things she was going to do to him after school, all of which were sexual in nature. My favorite part was when she said she wanted to, "Taste the Ronbow."
I was a second year teacher at the time and I really didn't want to make a big deal out of it. So, I got a red pen and corrected all of the grammar and spelling mistakes. The next day before her class strolled in, I placed it on the seat of her desk. She immediately knew I was the one who graded it. We never discussed it but I had very few problems with her talking the rest of the year.