THINX underwear are basically washable pads sewn into the lining of your panties, and they're an alternative to disposable tampons and pads. That's it. How well they work for customers depends a lot on the individual, but this isn't a consumer products website. They exist and they fulfill a legitimate market demand among the half of the populace that menstruates. THINX recently tried to advertise to this half of humanity by buying some subway ads in New York City, home to millions of riders a day. The response they got from Outfront Media, the group that actually sells the ad space seen by New Yorkers on their morning commute, was that they were too...icky. Here's an example:

*clutches pearls*

If you can't read the copy, it essentially says, with some rearranging:

Better underwear for women (or any menstruating human) with periods (shedding of the uterine lining).

Outfront Media didn't exactly say "no," but according to Slate, they wanted the whole thing toned down. Like, could it not be so much about periods?:

...An Outfront representative told THINX CEO Miki Agrawal that the ads with models “seem to have a bit too much skin.” And the ones depicting a peeled half-grapefruit or an egg out of its shell? “Regardless of the context,” Outfront wrote, they “[seem] inappropriate.”

Sources: h/t Slate