In the early '90s, the U.S. Fish and Wildlife Service had an opportunity to bust Victor Bernal, a Mexican zookeeper, on wildlife trafficking charges. But Bernal wanted to buy a gorilla, and using an actual gorilla for the operation was out of the question. What to do? Put a man in a gorilla suit and hope for the best!
Wildlife officer Terry English was chosen to get into the suit, on the basis that "the agent was fairly proficient at ape-like sound effects." The cage was then wheeled down to the airport and loaded on board Bernal's plane. They even scattered a few lumps of actual gorilla dung around the cage, partly for verisimilitude but mostly in the hope that the stench would keep the Mexicans from looking too closely at their purchase. And it worked -- totally fooled by the store-bought disguise, the smugglers transferred 95 grand to the suppliers, who immediately revealed themselves as undercover agents and placed Bernal under arrest.
The best part of the story was how Bernal was so fooled that he thought he was being attacked by a gorilla during the arrest! That's just one of six stories of outrageous capers that used ridiculous disguises, at Cracked. Link