A friend had a seriously silly quest: To find the best cheesecake in town.
On one of those nights where one gets dragged from place to place with copious alchohol, it happened: Placed in front of him was it. The cheesecake he always wanted.
The next morning no one could tell theme where they were, and he could never go back there again.
A true silly quest has this shape:
It is a search for nothing of true consequence.
With a climatic moment of attainment.
Never to be repeated again.
Most serious quests have this shape too. Which may make them silly.