Wiktionary
happy as a clam
a. (context simile English) Very happy and carefree. alt. (context simile English) Very happy and carefree.
Usage examples of "happy as a clam".
But then she was just as happy as a clam when she came back to pick up the watches.
I mean you'd be sitting over there on the other side happy as a clam wouldn't you?
And so, with a good dose of fan appreciation as appetizer, the ever-environmentally aware Barky settled right down with a medium-rare prime vege-rib and seemed as happy as a clam in unpolluted water.
Then you walk in with a pretty girl on your arm looking as happy as a clam.