If for whatever reason Bill Gates showed up on my doorstep, I have now formulated a plan in my head in which I will follow.
1. As soon as it is confirmed that it is Bill Gates, say, "Bill Gates, you have 5 seconds to turn around and start to leave this property. You have 25 seconds to complete that task. If you fail, I will use any force necessary to extricate you. Your time starts now". At this point I should glance at my watch to see the second-hand.
2. If Bill Gates is still standing there after 5 seconds (and possibly saying something), start counting down from 20 synchronously with the watch.
3. If Bill Gates is not gone, get nearest firearm and fire at will. If not, go back to posting on slashdot.