Vulgar libertarianism refers to those who treat the existing marketplace as one which closely approximates how a freed market would look. Kevin Carson quotes Studies in Mutualist Political Economy in his essay Contract Feudalism:
Vulgar libertarian apologists for capitalism use the term “free market” in an equivocal sense: they seem to have trouble remembering, from one moment to the next, whether they’re defending actually existing capitalism or free market principles. So we get [a] standard boilerplate article… arguing that the rich can’t get rich at the expense of the poor, because “that’s not how the free market works”— implicitly assuming that this is a free market. When prodded, they’ll grudgingly admit that the present system is not a free market, and that it includes a lot of state intervention on behalf of the rich. But as soon as they think they can get away with it, they go right back to defending the wealth of existing corporations on the basis of “free market principles.”
Libertarians will often condemn the existing aspects of state power and interference in the market but then leap to the defense of those who benefit from the existing order in the same breath. Conservatives are generally far worse on this front than libertarians but both groups shy from committing anything which smells like class warfare.
Roderick Long has recast this idea of vulgarity into the more descriptive and less polemical right and left conflationisms. A right conflationist is someone who defends existing property relations as being close enough to a free market to be considered legitimate. A left conflationist is someone who conflates existing holders of wealth as evil or undeserving a la “eat the rich!” The truth lies, as in most things, somewhere in the murky middle ground.
(And, as Jeremy Weiland is fond of saying, “let the free market eat the rich!“)