DiagnosTHIS is the adult party game where you’ll be dying to search your symptoms. Gameplay is simple. Each round, one player reads off a symptom card from the deck, and. the other players respond with their funniest Diagnosis card. Play until your heart’s content, or until it explodes. HYSTERICAL PARTY GAME: DiagnosTHIS is the hilarious adult party game where you'll be dying to search your symptoms! EASY TO PLAY: A hilarious take on the tried and true fill in the blank game that's perfect for game night at home, or taking on the road! One player plays a symptom card while the others play diagnosis cards, everyone ends up laughing..