Army Regulation (AR) 670-1 Practice Test

The main idea is that off duty, male soldiers have more latitude with jewelry, but it must still meet appearance standards. Specifically, earrings are permitted for males when they are not in uniform and are in civilian attire, provided the jewelry does not create or support ear gauging. The restriction about ear gauging prevents any appearance that suggests altering the ears beyond ordinary piercing.

So, wearing a simple earring off duty is allowed as long as it isn’t associated with ear gauges or other body modification. The other options don’t fit because the policy isn’t a blanket “no” for off-duty wear, it isn’t restricted only to civilian clothes, and it isn’t limited to exercise times.