I was in an exam last year and the boy a few tables in front of me got up and was walking past my table to the door to get out, just so happens the tables my school use have weird legs on them that stick out at the front, he managed to trip over mine and almost land in my lap. I was laughing for about 5 mins while the invigilator glared at me.
During my standard grades one of my friends was a few tables away from me and must of come to a question she had no idea about and went to cover her hands with her face but smacked herself in the nose and got a massive nose bleed.
Oh! I remembered one more, I had a friend that had an unconditional to university before he sat his 6th year exams so he hadn't bothered to listen once through out the whole year and was in his advanced higher maths exam and we were watching through this small window you can see through and he turned each page at a time, read it all, wrote nothing, slammed his head on the desk and got up and walked out. The funniest bit was the invigilator peeing herself laughing in the corner!