I have become a fan of this saying... it only took me 60 years to learn it, and only two years to say it without getting sick to my stomach. But you know what? I found it really causes me less stress than trying to sneek my way out of uncomfortable situations... and once it is said the person or persons causing me grief have a clear picture of my feelings. The saying is... wait for it... NO!
I say it politely, but not with an "I am sorry" because I am not. You have to stand for something or you end up standing for nothing.