[hamhamed]

You just say no man, it's that simple. Then you follow up with the reason.. (no, because I have a deadline for X project, and X gets delayed, we'll make less money..do you wanna make less money?) They hired you, so they trust you.

Obviously if you don't have a reason for your no, then you have to go with the yes. As a manager, I'd rather get a no instead of a 'yes' that ends up fucking up everything later because I wasn't aware of something.