Fred was a comic character who wore black singlet and gumboots he taught people how to laugh at themselves?

The character you're referring to is likely Freddie Starr, a British stand-up comedian, singer, and presenter who was known for his distinctive appearance that included wearing a black singlet and gumboots. Starr gained popularity in the 1970s with his risqué humor and catchphrase "Unbelievable!" In his comedy acts, Starr frequently made self-deprecating jokes and used wordplay, often poking fun at his own appearance and personal experiences. However, it's worth noting that while Starr often engaged in self-deprecating humor, he received criticism and faced allegations throughout his career regarding his jokes.