Maybe he ate some expired food from Walmart's shelves by mistake. If the food was contaminated or past its expiration date, it could cause diarrhea.
Once there was an old man in Walmart. All of a sudden, he felt a rumble in his stomach and then he had diarrhea. It was quite an embarrassing situation for him. He quickly tried to find the restroom in the store. People around were a bit shocked as they saw him in distress. He finally made it to the restroom, but it was a chaotic moment for him that he would never forget.
Maybe she ate something bad or got a stomach bug. Cartoons often use such situations for humor or to teach a lesson.
There could be many reasons. Maybe she ate some contaminated food like unwashed fruits or spoiled dairy products. Another possibility is that she has a food intolerance, for example, lactose intolerance if she consumed dairy. It could also be due to a virus or bacteria she caught, like the norovirus which is quite common and can cause diarrhea.
If the old man in the story was helping out other customers, like an old - timer sharing his wisdom on which products are the best value for money, that would be really interesting.
Maybe he got injured while playing or doing some adventurous activity.
Since I don't know the particular 'old man in walmart story', I can only guess. Maybe it was a story where an old man found a rare item on the Walmart shelves that he had been looking for for a long time. He was overjoyed and his excitement caught the attention of those around him, leading to a series of events that made it a memorable story.
Perhaps the other man did something wrong to provoke the old man. Or it could be part of a comical and exaggerated scene in the cartoon with no real reason.
It could be a side effect of a magic spell or some strange potion she took. In fanfics, all kinds of magical and fictional elements can be introduced, and an improper or misfired spell might disrupt her body's normal functions, including causing diarrhea.
The cartoon old man might have bad hair because of a crazy mishap in the story. Maybe a strong wind blew it all over the place, or he got into a fight and it got messed up. It could also just be a fun design choice to make him more memorable.
This is a rather unseemly topic, but one could imagine a situation where a cheerleader ate something bad right before a big game or performance. Maybe she had some spoiled food from a concession stand and her stomach started acting up suddenly during the routine, leading to an embarrassing situation with her pants.