ROFL!! My mother tried that with my brother, right under the arm. He started to scream bloody murder, "You're PINCHING me!" Poor woman was beside herself.
Do you and your son have a fairly consistant routine for the day? If you're kind of relaxed and easy going it might help to have more of a schedule. It sometimes helps when they know what to expect. My son behaved terribly when he was caught off guard by an unexpected errand, delayed nap or meal. And it would unsettle him for the rest of the day.