When one receives fellatio, whilest the partner with the dick in their mouth, is underwater. Derived from a pejorative term regarding the naming of towns throughout England, as they are named in relation to the river which they surround.
Newton Shill told his friend Ed Hype-Mantes all about how Liza Bootheecke gave him an underwater blowjob. He called it, stupidly and without purpse, New Castleing. Schmill died shortly after. No cause was given, but some speculate he was "too stupid too live."