Coup
When challenged, must you reveal the claimed character, or can you lose an influence instead?
The designer confirmed this on BGG, and the rulebook says a player who will not prove the claim loses the challenge.
You may refuse to reveal and lose an influence instead. The designer confirmed this on BGG, and the rulebook says a player who "do[es] not wish to" prove the claim loses the challenge. It keeps your card hidden, but costs you an influence, so it is rarely worth it.