Place popcorn and cashews in a large bowl. In a saucepan, combine corn syrup, butter, vinegar, and salt. Bring to a boil over high heat; boil 6 minutes. Pour mixture over popcorn and mix with a large spoon to coat. Let mixture rest until cool enough to handle.

2. Lightly coat hands with vegetable cooking spray. Place a few M&M's in the palm of your hand, and combine with some popcorn mixture. Gently shape into 1-1/2-inch a ball. Repeat with remaining popcorn mixture and M&M's.