The most interesting and important body language moment of Donald Trump's guest appearance on The Tonight Show was seen during Jimmy Fallon's preface.
Fallon: "Donald I, I wanna ask you 'cause the next time I see you, you, you could be President of the United States - I just wanted to know if there's just something we could do that's just not presidential really or something that, that we could do now that we're both just civilians .... like?"
Trump: "Like what? This is - I'm not liking the sound of this. Go ahead."
Fallon: "Could I mess your hair up?"
Incredibly as Fallon says, "... you could be President of the United States - I just wanted to know ...", Trump rotates his head and neck, stares into the middle distance and his face morphs into an expression of an amalgam of both regret and disgust.
Trump also maintains his low conventional steeple. This hand-arm configuration (which, when used for anything other than very short duration, projects arrogance and patronizing emotional tones) is omnipresent for Mr. Trump.
This facial expression is subconsciously generated. Most people would consider Trump's emotions of disgust and regret to be very counter-intuitive. And while it's possible that these could be for his feelings toward President Obama or Hillary Clinton - this wasn't the context of Fallon's preface.
Summary: Donald Trump feels regret and disgust at the idea he could be President.
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