I try to hide my pain.
While most folks will help you if they witness you being injured, and some folks will help you out if the see you in a cast and/or on crutches, nearly everybody eventually gets tired of the "cripple" who is always in the way.
I save my expressions of pain for when I really need them. It's kinda like how I use profanity - it has a greater impact when used sparingly; but when I must, I make the most of it!