Toph was bored. At this point in the day, she particularly enjoyed earthbending Sokka through a wall, but he wasn't here. He and Sparky had gone off fishing. She tried it on everyone else, but Aang didn't have the right reaction and Katara was being nitpicky and psychoanalytical. The Duke was too small, Haru could easily avoid it, and it just didn't feel right to toss a crippled kid through a wall.
Anyway, Toph was bored. She heard a badger-frog croak and reached out with her senses to see Aang doing his fire-fists and Hot-Squats one floor up, while Katara watched him from around the wall. An idea formed in her twelve-year-old mind. A master boredom-buster. The prank to end all pranks. The mother lode. Something that will be talked about for years to come. She smiled. This was gonna be good. For the rest of the day, Toph kept a constant toe on Aang and Katara.
Toph woke up early the next morning and walked into the forest. As part of her plot, Aang needed to be kept busy for a while. That meant trained Badger-frogs- or at least badger frogs that she can hit with tiny pebbles and force to croak. There Toph learned that Badger frogs were hard to sneak up on. After many failed attempts at tackling them, she settled for trapping their feet in the ground and carrying them into her room. With 5 badger-frogs cemented on her windowsill, she set out for the next part of her plot.
Just outside the Pai Sho room was a giant fountain. Toph and Haru had sparred together in the past,but never inside the temple itself, and around a fountain, nonetheless. Anyway, he was all too happy to oblige. Boredom had a way of spreading.
The two earthbenders took their stances, bowed to eachother, and began. Haru made the first move, lifting his left leg, and a spire with it, then kicking out with his right, jettisoning himself onto the roof as he did so. He hung there and watched as Toph easily deflected the projectile, then swiftly pulled a few rocks from the walls and launched them at him. He dropped from the ceiling and landed, leaving a few rocks of his own floating in midair. He knew Toph's style, and was finding ways to get around it. Keeping the rocks in the air as backup, He stepped back and jutted his arm forward, and a large furrow of earth formed and started traveling right toward his opponent. Toph moved to the side, and Haru brought his arms back and sent a spire from the wall directly at her. Toph blocked it again, as if she were annoyed by his attacking her.
Toph was only partly focusing on the battle. Constantly hitting the badger frogs in her room while keeping an eye on Aang and Katara was more than a little difficult. Taking the low road out, she formed a shield and sat waiting, keeping Haru boxed in by a heavy salvo of small pebbles. Katara was getting closer to the floor underneath them, and she was waiting on the right moment.
Unfortunately, Haru had other plans. He stomped on the ground, sending Toph's section of rock into the air and letting it hover there, and started pounding it on all sides. Toph was surprised, and quickly caved the floor in and fell out. Katara was in position. She punched the floor, and made a huge fissure. The floor broke, and Toph, Haru, the water from the fountain, and a considerable amount of dust all landed in Katara's general vicinity.
Katara was surprised. She was infuriated. She was every concieveable negative emotion that one could possibly feel without exploding or going insane. Most of all, she was covered in mud. Looking from the broken ceiling above her head to the two earthbenders on either side of her, she made a noise between a grunt and a yell and stormed off for her room. Toph watched Katara in her room, gathering her bathing implements. The plan was set into motion.
Aang was also in a state of negative emotion. Those damn badger frogs wouldn't stop croaking! His skin was hot and sticky from sweat, and his abs felt like they were on fire. He needed a bath. He went into his room to gather his towel and a change of clothes, and heard another croak. Ever the obedient monk, he performed his exercises, not caring to count out loud anymore, and started walking toward the bathroom.
Toph orchestrated them both perfectly. She needed to figure out how the hell to play Pai Sho. She would be unbeatable. Aang was stopped by another croak, and was unable to see Katara enter the bathroom.
Here it should be known that the bathroom at the Western Air Temple was literally a room where one takes a bath. The toilets were lower down to avoid any contamination. There were more that one, in the distant past, but they fell off due to erosion. Sokka had made a sign that said "Someone's in here." on one side and "No one's in here." on the other side to prevent any embarrassing situations. There were many before that sign was installed. Katara had turned the sign around before entering; Toph had turned it back around with a pebble.
Toph wasn't someone who would watch someone in the bathroom, but she had to see her masterpiece at work. Katara stripped down and placed her clean clothes and towel on a hook near the water's edge. She jumped under, and immediately stayed underwater and held her breath. It was a habit she had started when she was young, and a habit she unfortunately told Toph about. Toph slid the clothes off into a corner and watched as Aang came in and stripped off. When he was completely (an impressively, Toph noted) naked, and had placed his clothes and towel in the exact same place where Katara had placed hers, another badger frog croaked. He groaned, turned around, and started again.
Before he turned back around, Katara's hand reached out and grabbed his towel, and started drying her face with it. She stood up, stark naked, and unknowingly faced Aang. When she opened her eyes, she realized that this towel was orange, not blue, and dropped it immediately. Aang had turned a few moments before, and Katara was shocked to see Aang standing in front of her, stiff as a board (however that can be interpereted). Before they both emitted an ear-shattering scream, Katara noted that Aang's head was the only place that he shaved.