Why give him a break? He is a public CEO. If he does well the internet will talk about it. If he does otherwise, well, he can expect the internet to talk about it too.

Nobody gives a care if David is the coolest thing on his/your block. There is not one valid reason to tell a customer to "Please go away". You should just take the bullet, apologize for not meeting their expectation and maybe offer your point of view. If the customer is being rude, you have the right to not answer.