The same thing can be said about any other overused term among Leftists, like "fascist," "sectarian," "stalinist," or even "leftist." Without a precise definition, or some kind of broader context than cursing, or at least a few characteristics, we're left with vague jargon for a specific in-crowd. Its residual power derives precisely from that vagueness, and the people who throw around such curses haphazardly count on that vagueness and the emotive reactions of their audience.
The term still has concrete referents; it refers to people who wish for a return to some previous status quo ante where people knew their place, where the rich and powerful were accorded unquestioned deference and respect, where the unwashed masses knew they were to keep quiet, and where crazy ideas like justice and egalitarianism were the harmless pipedreams of professional philosophers, housebroken intellectuals, and other court jesters. Being a reactionary does not necessarily mean that such a person has a plan of action for turning back the clock; it's more a wistful nostalgia for simpler times of rigid hierarchy and unchallenged physical and psychic domination by patricians over the proles.