This idiom, considered informal and somewhat crude, describes someone who is extremely content, delighted, or in their element, as if a pig is joyfully wallowing in its preferred muddy environment. It conveys a state of unrefined, unpretentious happiness or satisfaction, often used in casual, humorous, or earthy contexts to emphasize raw, uninhibited joy. The phrase carries a tone of playful exaggeration, joviality, or mild vulgarity, reflecting cultural appreciation for vivid, unfiltered expressions and the human experience of pure, carefree pleasure. It resonates in relaxed or rural settings, capturing the exuberance of simple joys, and its animal imagery adds a layer of gritty, visceral humor, evoking a pig’s unapologetic delight. The idiom often celebrates unrestrained happiness, making it a colorful, if coarse, metaphor for being thoroughly content.

The phrase likely originated in 19th-century Britain or America, rooted in rural life where pigs’ contentment in mud or excrement was a familiar sight, symbolizing unrefined joy, as noted in farming folklore. Its earliest recorded use appears in a 1926 *The Saturday Evening Post* story, describing a character ‘happy as a pig in shit.’ The idiom gained traction in the 20th century, particularly in working-class and rural communities, reflecting a love for earthy slang, as seen in John Steinbeck’s *The Grapes of Wrath* (1939), which captures raw vernacular. Its use was amplified by mid-20th-century media, notably in American literature and films like *Deliverance* (1972), which embrace gritty expressions. The phrase’s adoption in British and Commonwealth English, especially Australia, came through American influence, and its spread was fueled by its vivid, if crude, imagery and applicability to joy, ensuring its enduring use in informal English-speaking contexts, from pubs to casual storytelling.