A term used to describe a person who acts like an activist, but from a metaphorical armchair — i.e., from a mostly or totally inactive, theoretical position.
Inherent in the meaning of armchair revolutionary is the idea that the person knows that their ideas require them to be physically involved in political struggles, but that instead the person chooses to be intentionally ignorant or dismissive of real-world issues and problems, in an attempt to continue believing in the false reality their views create. In this way the armchair revolutionary is often regarded to see the world in at least a quasi-idealist manner, i.e., one relative solely to his or her own perceptions, rather than bothering with what s/he should really do — to absorb the physical and practical reality s/he would be compelled to see around him/her if s/he stopped the alleged "political posturing" and became an activist in actual political causes
Jessica: The soup kitchen in our town closed down but we don't care! KONY 2012 WILL CHANGE THE WORLD!
Andy: Posting Kony statuses still? You're such an armchair activist.