15. 'The Gang Gives Frank an Intervention' (Season 5, Episode 4)
Danny DeVito joined the cast in the second season, and his Frank quickly evolved from a soft authority figure — father to Dennis, Dee, and possibly Charlie — into the new standard for just how disgusting a human being can be. Here, the kids decide that the old man's alcoholism just isn't "fun" anymore, and call on a therapist to help; they discover that the doctor is just as disturbed by how drunk and rude everyone at Paddy's is. Soon, the gang is springing "interventions" on each other for everything from Charlie's illiteracy to Mac's pathetic romantic life. The only one who remains un-chastened is Frank, who continues on with his plan: spending his remaining years on Earth by doing his best to "get really weird with it."