Levi Johnston's younger sister and Tripp's aunt, Mercede, will pose nude for Playboy, RumorFix.com is reporting. Levi demurely stripped for a 2009 Playgirl shoot, and now Mercede, 18, will reportedly take everything off for Playboy. "We're told Mercede will do what her brother didn't -- and show it all!" RumorFix reports.