This pejorative form sounds familiar to me from the US west coast too. As far as I understand it, the derivation is pretty much a conflation of WASP/blue blood/

This pejorative form sounds familiar to me from the US west coast too. As far as I understand it, the derivation is pretty much a conflation of WASP/blue blood/snob which kind of resonates with one thin American stereotype of Brits. Depending on context, I think it could imply the accused is infantile and/or positioned by nepotism...