Irony
Irony is a label that we gravitate to with ease but one that most would be hard-pressed to define. Because it involves complex linguistic and conceptual contortions, it is simplest to just assume that we will recognize it when we need to. It is that know-it-when-we-see-it quality, though, that has left irony open to opportunistic usage, defined by a given speaker based on his or her purpose at hand, used alternately as a convenient scapegoat, defensive shield, or badge of hipness.