A tweet can turn into a social media disaster for brands if not handled quickly, Alexandra Bruell writes. The usual tactics, such as issuing statements and apologies to counter bad PR, don't cut it in a world where trending tweets can quickly damage a brand, Bruell writes. Companies such as McDonald's have relied on humor to calm the storm. Others, such as Marriott, have had to rely on their communities to police themselves. While some tweets may not affect sales, they can damage a brand in the long run, experts warn.