One possible reason could be that he has a very weak bladder control. Maybe he's still young and hasn't fully developed the ability to hold it when he gets extremely excited, like if he's at a really fun event such as a circus with lots of amazing acts. Another reason might be that he has some sort of medical condition that affects his bladder function, and the excitement triggers the involuntary release of urine.
Perhaps he was so excited that he completely forgot about his need to pee. For example, if he was in the middle of an exciting game or competition and was fully immersed in it. His focus was so much on the exciting situation that his body's natural signal to go to the toilet was ignored until it was too late and he ended up peeing himself.
One possible reason could be extreme nervousness. When a boy is being punished, the stress and fear can cause his body to react involuntarily, leading to urination. Another reason might be lack of bladder control, especially if he is young. If he has not fully developed the ability to hold his pee, the anxiety from the punishment situation could trigger the release.
One reason could be that he was too engaged in an activity. Like the guy at the concert, he was so focused on the music that he ignored his body's signals. Another reason might be a lack of access to a toilet. The man on the road trip couldn't find a place to stop in time.
In some cases, she could have been given a lot to drink without realizing how quickly it would affect her. For example, if she was at a party and drank a large amount of liquid very quickly. Or she might have been wearing clothes that were difficult to take off quickly in case of an emergency, which contributed to the accident.
He can practice bladder training. By regularly going to the toilet at set intervals, his bladder can get used to holding more urine, which might help when he gets excited. For example, trying to hold it for a bit longer each time before going to the toilet.
Maybe the girl is just being mean. Some kids can be cruel without a real good reason.
One possible reason could be that they are just playing around in a rough and tumble way that kids sometimes do. Maybe they are siblings or good friends having a bit of silly fun.
One reason could be a weak bladder sphincter. If it's not strong enough, the pressure from laughing during tickling might cause involuntary urination. Another possibility is that she has a very sensitive nervous system, and the tickling stimulates the nerves in a way that disrupts the normal control of the bladder.
Perhaps in the fanfiction world, there is some sort of magical or technological device that mutes Naruto. This could be part of a plot where an enemy uses this device to stop Naruto from using his inspiring speeches or to isolate him from his friends. By muting him, they can disrupt his normal way of communicating and leading, which is a key aspect of his character.
In the fanfiction, Beast Boy could have eaten all of Raven's favorite snacks without asking. This simple act of thoughtlessness might set her off. Or he could have interrupted her meditation multiple times, which is very important to her. Also, if he was being too over - confident in a situation where Raven knew they needed a more careful approach, his cockiness could be a reason for her anger.
There could be various interpretations of a 'girl pees on boy story'. Maybe it was a situation in a play or a movie where it was a comical or unexpected moment. It might also be a real - life incident that happened due to some unforeseen circumstances like a lack of proper bathroom facilities or a childish accident. However, without more details, it's just speculation.