Grace Donald took a small baggie containing enough shampoo to completely affect the pool, after all it seemed like it should work even if diluted. She then went to the pool and when no one was looking she opened the baggy and submerged it underwater and dropped it. She then let osmosis do it's work as the shampoo solution started spreading around the pool. She then left and prepared for morning P.E. for some reason a lot of people didn't like swimming in cold water during the cold morning. At the very least she could give them something to get their blood circulating.
In the locker room as Grace was getting changed she could hear people talking behind her back saying things like "Why doesn't she just change in her swimsuit right at the pool, everyone's already seen everything already."... or maybe those were delusions. Either way she would get her revenge as the class went outside.
Outside the coach was telling everyone about the exercises they would be doing in the pool and freezing everyone's asses off. After listing a large amount of exercises we should do he said "Because we are so close to the holidays though... Go ahead and just play around in the pool." Some of my peers were happy and several of the guys and some girls jumped right in happy to try to have some fun. The rest of the class went into the pool a little more calmly. Thankfully the Shampoo was starting to bubble because of all the motion and you looked at the pool.
The coach asked "Grace you alright? Usually your the first person in."
You said "Just gonna wait a momment or two so everyone can calm down a little bit... Also the water looks a little... bubbly?"
the coach said "don't worry about it too much. Although I suppose you can wait for now."
You smiled internally thinking that you wouldn't be affected by the shampoo you put in. The shampoo you put in was...