Who made up clown clams as a idiom?

There's no idiom called "clown clams." It's likely a misunderstanding or a playful twist on the idiom "clam up."

"Clam up" means to become silent and refuse to speak. It's a common idiom used in English.

If you heard someone say "clown clams," they may have been:

* Making a joke: It could be a humorous way to refer to someone being quiet or shy, especially if they're acting like a clown.

* Using a made-up phrase: It could be a personal invention or a unique way of expressing an idea.

* Misremembering: They may have confused it with another idiom or phrase.

If you're unsure about the meaning of a phrase, it's always best to ask for clarification.