According to the American Heritage Dictionary, to whistle dixie is (to engage)] in unrealistically rosy fantasizing. Usually, it's used in a negative way...Don't just whistle Dixie, for example, means Don't sit on your ass wasting time. It comes from the popular southern song, Dixieland. See also, self-delusion, daydreaming, and/or bullshit. Your angel's whistling dixie!.