The excerpt below is taken from the entry on cromulent - to be found in a Wikipedia item on neologisms to be found on the Simpsons. I for one believe that cromulent is here to stay, and its use, whether with sincerity or irony (see below) is perfectly cromulent.
A word meaning valid or acceptable, coined by David X. Cohen for the Simpsons episode "Lisa the Iconoclast". When schoolteacher Edna Krabappel hears the Springfield town motto, "A noble spirit embiggens the smallest man," she comments she'd never heard of the word embiggens before moving to Springfield. Miss Hoover, another teacher, replies, "I don't know why; it's a perfectly cromulent word". Later in the same episode, while talking about Homer's audition for the role of town crier, Principal Skinner states "He's embiggened that role with his cromulent performance."
Based on the context in which Miss Hoover uses the word cromulent, we can interpret that she intends it to mean "legitimate", "applicable" or "appropriate." Principal Skinner seems to use it to mean "more than acceptable" or "more than adequate"; these usages would also (in an assumed lexical context) satisfy Miss Hoover's use of the word. Perhaps both characters intend it to mean "authentic", which would validate both uses of the word (e.g. "it's a perfectly authentic word" and "he embiggened that role with his authentic performance"). Lisa uses it later in that episode, when instead of telling the truth about Jebediah Springfield, she accepts that the myth and the made-up words have inspirational value. The word has a sort of recursive irony about it: as a made-up word it possesses none of the qualities that it describes.
Both "embiggen" and "cromulent" were quickly adopted and used by Simpsons fans. Cromulent has taken on an ironic meaning, to say that something is not at all legitimate and in fact spurious. Indeed the DVD commentary for "Lisa the Iconoclast" makes a point of reinforcing that "embiggen" and "cromulent" are completely made up by the writers and have since taken on a life of their own via the Internet and other media.