They don't understand much about christians... or the real meaning of the word, ably elucidated by Neal Stephenson, in Diamond Age in the mouth of one of his more interesting characters:
You know, when I was a young man, hypocrisy was deemed the worst of vices. It was all because of moral relativism. You see, in that sort of a climate, you are not allowed to criticize others - after all, if there is no absolute right and wrong, then what grounds are there for criticism? Now, this led to a good deal of general frustration, for people are naturally censorious and love nothing better than to criticize one another's shortcomings. And so it was that they seized on hypocrisy and elevated it from a ubiquitous peccadillo into the monarch of all vices. For, you see, even if there is no right and wrong, you can find grounds to criticize another person by contrasting what he has espoused with what he has actually done. In this case, you are not making any judgment whatsoever as to the correctness of his views or the morality of his behavior - you are merely pointing out that he has said one thing and done another. Virtually all political discourse in the days of my youth was devoted to the ferreting out of hypocrisy.
The truth of the matter is simple: a hypocrite is someone who advocates a standard in which he himself does not believe -- not one who advocates a standard and fails to live up to it. (There is a good case to be made that one who upholds a standard for himself and others while occasionally violating it is acting heroically, not badly.) Yet all the current accusations of hypocrisy lie in the latter arena, pretending to have evidence of the former in the curious thought that "actions reveal true beliefs", which would be anathema to a traditional understanding of people, in which "the spirit is willing but the flesh is weak" is a much more common thought. In other words, an accusation of hypocrisy pretends to an understanding of motivation and intention that only God could have, and use.
Which is why most of us, upon hearing someone assert that someone else is a hypocrite, assume that the accuser is the devil.
UPDATE: And, for extremists, acting consistently with your values is a sign of hypocrisy, which means that they are mentally challenged.