The term has been used for various things, but after 1995 (when AK Press published "Social Anarchism or Lifestyle Anarchism"), the term became a catch-all dismissal for any kind of anarchism that avoided and/or rejected the kind of muscular, serious, revolutionary, scientific or otherwise successful (?) anarchist projects that were being touted as the way forward for anarchism. In his creation of a category of disgust and hatred, Bookchin was (unconsciously?) echoing the Stalinism of his youth. Stalin and his acolytes could only blame counter-revolutionaries and saboteurs as the culprits for the failures of Stalinism; Bookchin and others who adopted the term "lifestylist" found a convenient bogeyman to blame for the unpopularity of anarchism. They are unable to acknowledge that there might be something in their kind of anarchism that turns people off. In the analysis of those who were targeted (both explicitly and implicitly), Bookchin's caricature was nothing but an incoherent jumble (how could one be both a yuppie and a lumpen? how could one be both an individualist and a fascist? etc). Sadly, plenty of anarchists (the serious, muscular ones) latched on to Murray's invention and insist on using it as a disparagement regardless of its internal contradictions; it is an easy (lazy) shortcut to indicate, as you said, anyone the person deploying the term disagrees with.