I'm a girl; my sister and I always try to embarrass each other anyway possible. I'd embarrassed her once before by filling her backpack with condoms (now don't tell me that's not embarrassing!), But one day after 1st period I had a whole soda of coca cola. I had to go extremely bad and my sister kept telling water jokes while in class and she kept making water pictures. I was then going to 4th period and my friend showed me a picture of a running river, and I just couldn't hold it anymore!!
I started peeing like crazy! So much that a stream was shooting off my pants and it was like 5 inches big...After that I felt good but all my clothing was soaked and I was still dripping I got red in the face and was being laughed at.
That was a day I would never forget, and I swore that I would get her back.
And I did - by filling all her underwear with petroleum jelly!! ;)