You've never been hanging around a bundle of CEOs in the City when one of them said, "I know! Let's have an impromptu barbeque near Fleet Street!" It's perfectly common.

(Actually, I could see an investment banker trying to do that in Central Park, hoping the entire thing would go all Dejuener Sur L'Herbe (http://en.wikipedia.org/wiki/Luncheon_on_the_Grass) on him...)