My class was being talkative in Physics, and my teacher (being one of those who has no idea how to control a class) was saying 'please quiet down' 'quiet now' 'shush class' and i said 'no sir, thats not how you do it, listen, then i screamed 'SHUTTT THE FUUUUCK UP !!!!!' as loud as i could, and my class, and a few others nearby went quiet.
I got a rather long detention with the head of science who's a fat women with a moustache.. but it was so worth it to see the look on his face. Especially as it actually worked
Another one was when me and my friend made a massive explosion in chemistry with powdered magnesium by accident. I didn't quite grasp how volatile it is, and poured a whole load into a bunsen burner, and a massive flash followed that scorched the ceiling.
Year 10 science was awesome.