The one where the people of the US elect a Muslim as president and...
Oh.
Wait.
LOL! Number 1 nightmare episode!
"Apparently benign alien emissaries show mankind how to end the misery
of war, plague and famine. The Kanamits, nine-foot tall aliens, arrive on
Earth with one lofty goal: To Serve Man. They end war, they end famine.
They make the military wonder: what's the catch?"