Several years ago I was at a party talking to a girl I was not romantically interested in but wanted to get to know. We were discussing a subject of mutual interest, and both of us were slightly nervous.
Suddenly a great BANG! came from outside and I turned to the window. Nothing.
In that split second she had turned her head, interpreting my surprise as a calculated sign of disinterest, and another girl she was well-acquainted with now held her attention. I wanted to protest that I'd been caught off guard and wanted nothing more than to talk to her, but it was too late. A mere forty degrees had created an impenetrable barrier to all rapport.