South Park Episode 610 - "Bebe's Boobs Destroy Society"
Mr. Mackey punishes the boys by forcing them to join the "Getting Gay With Kids" choir.
The choir is going to Costa Rica to help save the rainforest. While on a tour of the rainforest the choir group gets lost when a snake kills their guide. They soon discover the evils of the rainforest, which changes the choir group's message.