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general::
Also, happy as a lark;happy as a clam (at high tide). Extremely glad, delighted, very cheerful, as in He was happy as the day is long, or When she heard the news she was happy as a lark, or Once I got the test results I was happy as a clam at high tide. The first of these similes dates from the late 1700s. The second alludes to the lark's beautiful, seemingly very happy, song. The third, from the early 1800s, alludes to the fact that clams can only be dug at low tide and therefore are safe at high tide; it is often shortened to happy as a clam. happy camper A satisfied participant, a contented person, as in She loved the challenge of her new job; she was one happy camper. This expression is Also often put in the negative, as in She hated the heat and humidity of the southern summer; she was not a happy camper. [Slang; mid-1900s]
American Heritage Idioms