My first hope is that the smell of the crap in my pants would be enough to chase him away. If that doesn't work then I pray that I am mentally prepared and steady enough to use my weapon to defend myself and others.
If I see anyone pull a gun the very first thing I am going to do is find some HARD COVER. Come and get me sucka! Anyone else in the area who could have chosen to excercise their right to defend themselves but did not - you're on your own. Call 911.