Physics was my favourite followed by Chemistry and lastly, Biology. Both Chemistry and Physics had some hilarious moments. This one time in Physics we had these polarised sheets and you had to put two sheets perpendicular to each other to get the polarized effect. So we were looking at the sun and one of the guys goes "hey, is the sun really purple?" and he moves the sheets away from his eyes and all you can here is "Arrrgh!" and the whole class burst into laughter. Another time we were all flicking pens around and I wanted to join in the fun! So I grabbed a pencil and I was aiming to flick it into the trash can at the other end of the room. I flicked it too high though and it hit the ceiling then smacked my teacher right in the face. The rest of the class were trying to hard not to piss themselves with laughter as the teacher raged at me. I was just like how the hell did this happen >_<.
As far as Chemistry goes, we did this experiment with a Bunsen burner and there were two beakers - one filled with water and the other with ethanol. This girl lights up the Bunsen burner and then leaves the match on the table. So the table slowly gets caught on fire and she's like "oh no!" and grabs the beaker filled with ethanol and splashes it over the fire which only makes the fire five times as large as before. Fortunately the teacher rushed in and resolved the issue before it got any worse. Another time we were setting up the equipment for this experiment and the flask me and my mate picked, had a cork stuck in it. He tries to pull it out but fails and then I'm like "give it here, a man's strength is needed" and I take the flask and try to pull this cork out. Even I had to admit that this cork was properly stuck. So I tried again using all of the strength available to me this time and I ended up ripping the cork in half and pulling the top part of it away so that the bottom part was still stuck in the flask. We just looked at each other in disbelief before going to the teacher and handing the flask to him. He looked at me and asked "how did you manage to do this?" and I was just like "I don't even know".
I have loads of other stories but I won't bore you with any more lol.