happy as a pig in mud

To be happy as a pig in mud is a way to show how very happy you are since pigs in the mud are often very excited and pleased to be in the mud. The phrase is another way to say like a kid in a candy store. Happy as a pig in mud is usually in reference to someones frame of mind during a specific situation in which they are very pleased with the way something has turned out, and very excitable as a result.