sitting in a bath tub full of bubbles listening to sad music and crying for no reason

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

The act of ditching your friends to have sex with your mom, or because you are afraid of being prison raped like your dad was.

When taking a bath, you are literally soaking yourself into your own filth.

When applied in a more metaphorical sense, it means to embrace the dirty and imperfect side of you (that is stigmatized by society).