Every so often my daughter's principal would call me for an emergency substitution at the nearby middle school. Mainly because I lived a block away and he knew he could call me at the beginning of the school day and I'd be there before the first class session began.
The one time I subbed for a math class, the teacher had left a boring problem sheet for them to work on. Instead there were spitballs. so many spitballs. (this was the only class I had that problem) So many that I could Not figure out where they were coming from to pick one or two students to blame, so when, at the end of the class they had not completed that dinky sheet of math questions I told they they had to complete it over the weekend. (AW, Mrs. Old. we never get homework over the weekend.) And that I was leaving a note for their teacher explaining why. (leaving them to wonder what punishment the real teacher would give them for the rain of spit balls.)
Actually, I had problems keeping a straight face during that class, because I thought it was hysterically funny.