When used with ellipses, the act of showering becomes an insinuation of masturbation. When spoken, a pause is used and the voice is lowered to tacitly convey the message.
friend 1: Is that a wocket in your pocket or are you just happy to see me?
friend 2: Brb...shower...
friend 1: What are you doing with that magazine riddled with scantily clad women?
friend 2: I'm going to go...shower...to it.