The act of wasing one's hair (on one's noggin), and applying the leftover shampoos to one's pubic hair. May sometimes be carried out for masturbational purpose rather than for hygienic one. Believed to be carried out often by a Jacob, and possibly by a Thomas.
Mum: What the hell were you doing in the bathroom for the last 30minutes!!??
Jacob: What the hell mum, I needed to shampube.
When you wash your hair (with shampoo) and the shampoo has gone down your body and gathered up in your pubic hair. Sometimes you will notice when you have gotten out of the shower, meaning you have to get back in to rinse your pubes.