That moment when your project manager says to the client "That is clearly possible". After that he asks you if that is in fact possible to do, you say: "is possible with major limitations" and then he understand they screwed up but in the end the one that is screwed up is you.

If I could give you more than one ++ I would, I am going through this right now except the promise was made before asking me if it was possible. It's due last week and I still don't know the new specifications to even try to see if it is possible. I warned then that they likely made a promise I'm not going to keep and I have no problem laying the blame where it goes on this sort of thing.