I can understand that this might be a sensitive and personal issue for some people.
In human relationships, feelings about others seeing one's underwear can vary widely from person to person. Some individuals may feel embarrassed or uncomfortable with such situations, while others may not be bothered by it at all. It depends on cultural norms, personal boundaries, and the level of comfort and trust in the relationship.
If you find yourself in a situation where you feel uncomfortable changing clothes in front of a friend, it's essential to communicate your feelings and set appropriate boundaries. Respectfully let your friend know that you prefer some privacy while changing and explain your reasons if you feel comfortable doing so. A good friend should understand and respect your boundaries and feelings.