Excerpt from this article:
Historically, the bathroom selfie used to be perceived as fairly cringeworthy. If you had to take a picture of yourself in the bathroom mirror, camera flash obscuring half your face, it implied you had no friends to do it for you. But the bathroom selfie has evolved – as the million-plus hashtagged Instagram bathroom selfies attest – a shower selfie also proves how good you look without makeup, sticking a leg out of bathtub bubbles gives you the chance to flash some flesh while pretending not to be too craven in your attention-seeking. At the Met Gala Ball, the bathroom was where people went to take the selfies that had been banned by host Anna Wintour, the modern celebrity equivalent of smoking in the loos at school. The most interesting bathroom selfies are political. In the US, transgender people have been taking selfies in public lavatories to protest against laws which insist they use the bathroom of the gender they were assigned at birth.
But for most, a bathroom backdrop is simply an alternative to the golden sunsets or plush bedroom suites that already litter Instagram’s most epicurean snaps. “The essential psychological motivation is always going to be some form of validation,” says Aaron Balick, author of the Psychodynamics of Social Networking. A bathroom selfie is no different. Although, he points out, a bathroom provides a feeling of privacy in which to photograph yourself, at odds with your decision to share it.