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1.
A combination of "Dumbstruck" and "Pun"

Thus, "Punstruck" is to be dumbstruck or confused by a pun.
Al: "Whale Whale Whale, What have we here"

Yang: "what?"

Al: "It's funny because the word Whale sounds like Well, and it's a common phrase when people say 'well well well' so it's a pun."

Yang: "I'm punstruck"
by AlanG-LeAngryBirds December 19, 2012