dodyskin nailed the def as I always understood it. I always assumed it was a UK coinage. The only thing I might add is the connotation that these be-dreaded trust-fund-babies were marking time until real life kicked in. Most of the ones I knew eventually sobered up and became precisely the corporate tools that they had previously denigrated.
Im my local punk scene, the same type of poseurs were referred to as "credit card punks."