First of all, despite the title, I want to state that I have nothing against MS-Word in general; it is a great program, in general terms.
But one so-called feature in Word has made me despair more than once. That is the feature in which Word automatically selects a style, based on the format of a text. As a result, you will often see text marked, for example, with the style "Header 7", when the text was not meant to be a header.
Of course, I have turned this "feature" off, as well as a few other features (1). But there is really not much I can do about it: the problems usually appear with other people's documents.
(1) A "feature" that is really dangerous is to automatically apply suggestions from the spell-checker. If you are not paying attention, Word might replace any nonsense for a mis-spelled word - or even for a word it simply doesn't find in its dictinoary. Perhaps this one should receive the honor of being called the "worst feature"?
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)