Divide into groups of 3 or 4.
Each group gets a balloon covered in shaving cream, and a razor. Their job is to shave the balloon. First group to complete the task is the winner.
The trick is - when the balloon breaks, the shaving cream goes everywhere, so be prepared! A little nick on the razor's edge before hand will assure that the balloons will break.
A variation: The "Water Balloon Shave"
Split into couples (guys/girls) - the guys come to the front of the room and sit in chairs facing the audience. Each guy has a large water balloon on their heads. The girl partner(s) cover the balloons with shaving cream, and with a single edged razor blade (no razor, just the blade) try to "shave" all the soap off of the balloon without breaking it. Whoever is the first to succeed is the winner.