D..
You couldn't have bribed my boys to wear boxers. They hated them. They were on the swim team, and yeah, the boys saw what everyone wore, and yeah they got teased. They'd throw some snarky comment back making fun back at the kid teasing them (well at least I've got hair on my legs, and not chicken legs) or something like that to deflect it. They knew they weren't changing wearing what was comfortable on account of butts on the swim team...
The only underwear rule I had was that they wear some form of it...
Now, using top sheets on their beds? That's a battle I didn't win...lol!