Happy as a pig in muck

Origin

For centuries, those who lived alongside livestock observed a curious paradox: while humans naturally recoil from mud and grime, pigs revel in it. A pig's skin lacks functional sweat glands, making a cool, thick layer of muck its natural air conditioning, sunscreen, and insect repellent all rolled into one. Watching these intelligent creatures roll, root, and snort with evident pleasure in what to us is a filthy mess, the image of absolute, unadulterated contentment became indelibly linked to this earthy behavior. The phrase thus crystallized from this simple, vivid observation of nature, capturing the irony of finding immense joy in the grimiest of circumstances, a stark contrast to human sensibilities.