In fact, Obama's comment, that his audience shouldn't boo but should instead make sure to get out the vote because "voting is the best revenge," is a takeoff on a centuries-old quote by 17th century poet George Herbert in Jacula Prudentium: "Living well is the best revenge."
His message: Be voter, not a hater.
Frankly, people who are going off about this are revealing their utter ignorance of our Anglican-influenced culture — even though it's often the same people who hold up our Anglo-American heritage as the supreme identity of the United States. (I'll admit, though, that I first learned this quote from watching an episode of Frasier, where Frasier suggests to his brother Niles that their comfy existence in Seattle high-rises was revenge enough from the high school bully who they'd encountered anew when he showed up as a plumber to fix Frasier's bathroom.)
Meanwhile, Romney himself offers "love of country" as a counter to "Obama's revenge." Romney's insistence on "love of country" versus "revenge" is made even funnier by an 18th century quote made famous by Samuel Johnson: "Patriotism is the last refuge of a scoundrel." (For those of you in Rio Linda, patriotism = "love of country.")