The key is not to let the leader feel humiliated by any means, why not let him/her know your idea... But I suppose talking against the leader not in the presence of other coworkers is crucial.

A saying, which might fit here some how: "you may come to your boss with your own ideas, but you must leave with his ideas"

You can do what you like.I understand in China if you talk against your leader they might throw you in prison.

Oh, I should add that I understood this to mean national leaders. You must use more diplomacy and respect with a supervisor at work but same rules apply.

I think leaders with malformed or simply wrong opinions SHOULD be humiliated. It's seen as a virtue in many nations to question authority. It doesn't serve to undermine leaders; it makes them justify their reasoning and prove why their way is the best- not simply 'because I said so, and I'm the boss'. I understand this is difficult in some countries.