I had a guy stop in front of me coming into the grocery store last week. He was deeply entranced with a text he was crafting. After counting to 10, I said "any time you're ready - because clearly you work for the President and it's important - so I'll wait."
He came to, turned around and glared, then immediately decided not to say anything and move on.
I think that it may have been the "Go ahead, make my day" look on my face that turned him back around and got him moving.
Life is too short to suffer idiots and fools.