Definition & Meaning of "happy as a pig in shit"in English

What is the origin of the term "happy as a pig in shit" and how is it used?

"happy as a pig in shit" is an English simile that dates back to at least the 19th century, using the image of pigs wallowing in their own excrement to convey extreme comfort and contentment. The metaphor draws on the observation that pigs appear to enjoy being in their messy, natural environment. The phrase is used in informal speech and writing to describe someone who is very happy or satisfied. It is mildly vulgar due to the reference to excrement, but it is generally considered humorous rather than offensive.