Princess Pot Luck
Any party should have food for its guests, and a "Princess Bride" activity party is no exception. Invite everyone to bring a dish to share in the theme of medieval fairy tales. This might be "Fire Swap dip" (an average taco dip) or a Princess cake with lots of decorative frosting. Drinks could include mead (if your guests are over 21) or birch beer. Julie, a blogger at "That and This," suggested serving the "pizza of unusual size" and "shrieking eel cutlets."
Rhyme Time
"No more rhymes now, I mean it!" "Anybody want a peanut?" One of the more memorable scenes in "The Princess Bride" involves Inigo Montoya and Fezzik the giant rhyming to irritate Vizzini. Playing an around-the-room rhyming game, where each person has to continue to rhyme with the person who spoke ahead of her, is a fitting activity for this scene.
Switching the Punch
When Vizzini attempts to outwit Westley, our hero, in a game of wits, he loses by drinking the poisoned wine. You can play a similar game (without poison!) by switching around small cups of punch. Take turns either moving the cups around, or using riddles, to trick your friends into drinking the poison (for safety purposes, use vinegar or something else non-toxic but unpleasant).
Trivia
If you're with a group of people who are big fans of the film, trivia is a fun way to interact with the content. Find a collection of user-generated quizzes online, or make up your own questions.
Fencing
Even if you're not as experienced as Westley or Inigo Montoya, there's never a dull moment in a sword fight. Use plastic swords--which you can get at any toy store or dollar store--to fight your friends on your own "cliffs of insanity" (in this case, tables and chairs).
Watch the Movie
Don't forget to watch the movie, yell out your favorite quotes, and re-enact your favorite scenes. Having a "Princess Bride" activity night without involving the film is inconceivable!