The feeling you get after drinking too much liquid and you can hear the sloshing in your belly. The sound you used to try and hear when you were little and had too much luquid to drink.
Canadian rapper Maestro can be credited with coining the term although now popular amongst various rappers such as the Ying Yang twins.
After pulling a prank in a public washroom which involved leaving an unsightly item in a urnial, Maestro passed a local patron, patted him on the back and said "Its all yours, Billy Ocean"
-Billy Ocean is the Canadian equivilant of Nah Mean or Nam Sayin
-Can also be used to sum up a situation, moment, mood or feeling
-In place of nah mean:"Yo, the washroom is all you, Billy Ocean."
-As a description: "That cat had me straight vexed like Billy Ocean"