Take a piece of yarn and tie it in to a necklace. Give each person at your party a necklace as they arrive. Instruct players that they cannot say "yes", "yeah", "yup", "uh-huh", "si" or anything that means yes. The only thing they can do it shake their head to mean "yes". Everything else is considered saying it. If a player hears another player say "yes" or one of it's derivatives, they can take their necklace(s) from them (if a player has several they have to give them all up) and they become yours. The person with the most strings by the end of the party gets the prize.