I remember once I brought some stink bombs into school, and we decided that we'd let one off in the middle of our History lesson.
So we got it out, put it on the floor set it off, then continued with our work as if nothing had happened, desperately trying to contain ourselves.
It was so hilarious looking around the classroom and seeing everyone's reaction as they eventually became aware of the foul odour. "Has someone got egg sandwiches?!" someone said. After a few minutes the entire classroom was complaining of the stench and we were literally in tears with laughter.
Anyway eventually we were caught and paraded in front of the entire school during assembly. We were insulted and compared to Saddam Hussein by the deputy headteacher before being issued detention. Oh those were the days