I agree with Br Irfan's post but, you are right, there is much room for politeness. Thanks!
However, the Qur'an does not admonish us to be dumb and mute.
Call a spade a spade. There is no mockery here. Please read carefully.
2:42 Do not confound the truth with falsehood, nor conceal the truth while you are well aware of it. [2:159, 3:71]
2:159 Indeed, those who conceal anything of the evidence and the guidance that We have revealed after We have made it clear to mankind through this Book; such are the ones whom God will condemn and whom all who have discernment will condemn.
3:71 O People of the Book! Why do you cloak the truth with falsehood, and conceal the truth that you are so well aware of?
Also, please know that KUFR also means keeping quiet to conceal the truth.