There are some images under there that aren't panties though, but they are in the great minority and some have their own tags.
post #360908, boxer shorts on head, which we don't tag as panties.
post #395552 buruma on head.
post #363192 bloomers on head.
buruma does have the very empty buruma_on_head tag, and bloomers has blomers_on_head. The boxers example though doesn't have it's own tag.
I do question if it is necessary that each similar garment requires it's own specific *_on_head tag and couldn't be replaced with like a underwear_on_head tag, but in the case of panties it does overwhelm any other garment that would be under a more general tag.