Allowed product, narrow camera
Men's underwear is not a restricted product. Meta's health and wellness page exempts lingerie, swimwear and undergarments from its 18+ targeting requirement, provided the ad does not violate the Adult Nudity and Sexual Activity policy. TikTok does not ban the product either. Its adult content page instead lists what the creative must not show: clothing that exposes or implies exposure of intimate areas, emphasis on sensitive body parts or regions, sexualized body positions, and stripping or undressing.
For men's underwear that list lands in an awkward place, because a lot of what the category sells (support, shape, a contoured pouch) lives exactly where TikTok says not to put emphasis. The job is to explain those features without pointing the camera at them.