Note to self: Self, if you're ever put in charge of a citywide ad campaign, don't say mean things about neighborhoods in that city. Not even if it's Cincinnati. Purina learned this the hard way when a billboard in its "No More PU" campaign for Tidy Cats cat litter compared Over-the-Rhine, a notoriously rough Cincinnati neighborhood, to a used litter box.  The billboard read: "You're so over Over-the-Rhine" next to the campaign's #lifestinks Twitter hashtag. Naturally, the local response was less than kind. One Facebook user even compared the billboard to "a bully on the school playground," which is an apt comparison. Purina later apologized. How about no more PU in your advertising, Purina?