Yes, you probably know what a HIGH FIVE is.
In the picture, I want Kevin to give me a HIGH FIVE. I have raised my hand and I want him to raise his and slap mine. But Kevin is not responding.
By ignoring me, Kevin is LEAVING ME HANGING. When we LEAVE something or someone HANGING, we are leaving that thing waiting to be finished. The expression we use when this happens is, "Don't LEAVE ME HANGING!"