Okay, I researched this question. There are several “toilet costume” groups on Pinterest and toilet costumes for sale as seen in Google Images, however at this moment it appears there isn’t a (commercially produced) sexy toilet costume as yet – but this does not rule out there being a home-made version which has not yet become part of either of those locations. Make it so!
I did however find a sexy urinal. It’s actually a wearable form of the art piece “Fountain” by Marcel Duchamp so its intent/purpose was not precisely what you had in mind even if the content itself technically is that very thing.
I hereby admit my intrigue in how there are costumes representing artworks. Anyone can be Mona Lisa but how about a Warhol can of soup, a Van Gogh swirly post-impressionist image, or a Mondrian set of color squares?