What is the most frustrating puzzle you have ever encountered?

I’m talking about the kind of puzzle that finding a solution will only make you more angry about its arbitrariness.Broken sword has The infamous goat puzzle, Owned by Gabriel Knight 3 Cat fur mustache puzzle. If your adventure game puzzle has a full Wikipedia page, that might not be a good reason, is it? Other obvious contenders include the Babel fish in The Hitchhiker’s Guide to the Galaxy, the cream pie in King’s Quest 5, the cream toilet in Discworld (don’t ask), and the 10 worst and worst adventure games in our list. Everything in the serious WTF puzzle list.

What is the most frustrating puzzle you have ever encountered?