A bathing machine. You cannot honestly tell me that in your youth you have never gone to the sea with your friends without the need of a bathing machine. If not, then I may be inclined to believe you to really be a woman in disguise, in spite of the hair on your face.

[Bathing machines are, after all, unnecessary in the company of other men. It's only a formality, one which Grantaire is all to happy to ignore.]