Just for fun....
Ben Witherington remembers a funny example of an impromptu prayer gone wrong.
I remember a particular Thanksgiving dinner at my aunt's house in Statesville, North Carolina, where, as we were all sitting down, she asked my father to pray impromptu over the meal she had been preparing for many hours. Somewhat flustered and unprepared, he prayed, "Dear Lord, please bless our sins and pardon this food in your Son's name. Amen." He would not soon live down that blessing.
Making a Meal of It (Waco, TX: Baylor University Press, 2007), 17-18