I got this idea from a friend of mine at Camp Orchard Hill, Derek Hodne. I did some searching online and discovered that many other people have taken this game and packaged it into various retail forms, such as Watch Ya Mouth, Speak Out, and Mouthguard Challenge.
The game is simple, and you can do it yourself with a small or large group setting with a little creativity. The supplies needed are the plastic mouth spacers (cheek retractors) that dentists use to hold back lips and cheeks while they work on patients. You can grab a dozen of them on amazon.com for about $12 ($1 per spacer).
You give a player the spacer and they put it in their mouth. Then you give them a phrase to try to say and the other players have to decipher the phrase. The spacer makes it near impossible to pronounce words with sounds like “M”, “B”, “P” or other phonetics that bring the lips together. So phrases like, “Mommy buys peanuts at the market” can be both difficult and entertaining at the same time.
When my friend Derek administered the game, it was at a gathering of hundreds of high school students. He called up about eight players onto the stage and split them into two teams of four each. Each team had one player with the cheek retractor and the other three were the phrase guessers. It was fun for the rest of the crowd to watch as Derek held the microphone up to the teams while they played.
Try it with your group (large or small) and have fun!