The story
From happy as a clam at high water/happy as a clam at high tide (a clam at this time would be difficult to catch).
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: Very happy and carefree. Full definition →
From happy as a clam at high water/happy as a clam at high tide (a clam at this time would be difficult to catch).
Etymology from Wiktionary, CC BY-SA 4.0.