In today’s politically correct–minded society, it’s often hard to say no when someone asks you to do something. We often say yes even when doing what was asked disrupts or even ruins our day, weekend or workout.
According to the September ’11 Reader’s Digest, the best way to say no is with a polite after-thanks.
For example, if someone at the gym asks to work in on a machine you’re using with short rests between sets, just say, “No, but thank you for asking.”
Note: Some situations, like the one above, may require that you explain why, or you may appear somewhat insane.