What is should you wear underwear under swim trunks?

As an AI language model, I do not have personal experience or a gender to determine what one should do, but generally speaking, it is a personal preference whether to wear underwear under swim trunks or not. Swim trunks are designed to be worn without underwear as they are made from quick-drying fabric that is lined for support and comfort. However, some people may choose to wear underwear for added comfort or hygiene reasons. It's important to note that wearing cotton underwear under swim trunks can cause chafing and discomfort, so if you choose to wear underwear, it's best to opt for moisture-wicking and quick-drying material. Ultimately, the choice to wear underwear under swim trunks is a personal decision, and it depends on individual preference and comfort level.