It is a snippet taken from a Donald Glover stand-up special (titled "Weirdo"). The collar pull (which is what he is doing) is an age old piece of body language that indicates discomfort. An exaggerated version of the collar pull is often used for comedic purposes. In this instance, it is being used as a gesture of "dramatic irony" (a narrative device for when the reader/audience has more information than the character in a novel/play). The implication is that you are in for an unpleasant surprise.
;)
Oh wow i didnt expect this elaboration. Thanks a lot for explaining. :)