Libtard n. Portmanteu of "liberal" and "retard". Someone who, intoxicated by being knowlegable and right about politics and economics, forgets that they need to get actual real ordinary people to support them if their agenda is to be advanced. Often but not always rich, well meaning and with good insight to society's problems, but naive about the mechanics of politics and utterly ignorant about how power actually works.
"Them libtards at the Occupy protest are going to get stomped by the riot squad because they're too smelly and weird for ordinary people to support them. Sad really; they're right about pretty much everything but they have really shitty PR."