In the Season 2 premiere of Two and a Half Men , titled " Back Off, Mary Poppins ," Charlie's exclusive, star-studded support group is disrupted by Alan's desperate attempts to join in. The episode features memorable guest appearances from Sean Penn and Elvis Costello as they discuss their lives with Charlie, while Alan's uptight personality clashes with the group's relaxed vibe. This standout episode, which highlights the show's signature humor and character dynamics, originally aired in 2004.