小猪喜欢在泥巴里滚来滚去，虽然弄得一身脏，却乐在其中。表达 “as happy as a pig in muck“ 就借这一情景来比喻一个人 “高兴得不得了、乐不可支“。这个说法多用来描述因自身情况或目前的状态而感到非常高兴，而不能形容因为某件具体的事情而开心。
除了 “as happy as a pig in muck“ 以外，也可以说 “like a pig in muck“，意思是一样的。
Paul had started to hate his job, so he changed career path – now he’s as happy as a pig in muck.
Noah loved his birthday – surrounded by his family, friends and lots of presents, he was like a pig in muck.
On her day off, sat enjoying a leisurely coffee and curled up with her favourite book, Alice was as happy as a pig in muck.