When a ship 'Crosses the Line' it signals the start of ceremonial practical jokes. Those who have not crossed the Equator before are summoned before the Court of Neptune. Neptune was the Roman god of the sea, equivilent to the Greek god Poseidon. He is usually depicted as a bearded elderly man of stately stature carrying a trident, usually seated on a throne but also seen astride a dolphin or a horse.
Once before Neptune the supplicants are sometimes ducked by bears, roughly lathered and shaved. This is now usually a good humoured affair but in times gone by the horse play was supposed to be a bit rough on the participants.
As far as I know this is now only carried out when Crossing the Equator but was formerly carried out crossing the 39th parallel, going through the Straits of Gibraltar and rounding the Cape of Good Hope.
See what I mean by roughly lathered and shaved ?