While one's choice of fashion is not, in a pure sense, body language - the Venn Diagrams describing these two phenomena overlap. Moreover, few men fully appreciate the level of double standard society places on women and the clothing the "should" or "shouldn't" wear (or what wrinkles should or shouldn't be covered). In addition, styles vary from year-to-year and from country-to-country. Still, even taking all of these factors into account, Hillary Clinton should absolutely NOT be wearing high-collar shirts.
In many countries - and certainly North America and Europe, high collared tops covering significant portions of the neck - particularly the front of the neck - send messages of low-transparency, closed-mindsets and clandestine motives. While this is of course, not always true - it is how many will interpret it (country exceptions include India and China). As with 99+% of nonverbal behavior, the implication of secret keeping doesn't pop into one's minds eye in neatly typed bullet points - rather it's perceived subconsciously or at the edge of consciousness.
This same clothing-nonverbal principal also holds true for men - but somewhat less so. For although men are "allowed" to wear ties - such style should not be over-played. Any images of Adolf Hitler or Benito Mussolini with the front of their necks exposed are practically nonexistent. And although their countries certainly play a role - this is just as true with Kim Jong-un, Mao Zedong and Pol Pot. There's no escaping the fact that a large percentage of Americans will associate images (via conditioned response [e.g., remember Pavlov's Dogs?]) of these tyrants with either men or women who cover their necks so completely especially in this same fashion. It's not fair, but it is true.
Thus if Mrs. Clinton wants to build rapport with the electorate - and send messages of trustworthiness, openness and transparency she should (among other things) stop wearing this high collared style.
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