How do you get a stomach ache on purpose?

How do you get a stomach ache on purpose?

We get stomach ache due to the following reasons:- 

1. constipation.
2. diarrhea.
3. gastroenteritis (stomach flu)
4. acid reflux (when stomach contents leak backward into the esophagus, causing heartburn and other symptoms)
5. vomiting.
6. stress.