Did you ever wonder where the pinching tradition started?
It's thought that the pinching started in the early 1700s, about the time that awareness of St. Patrick's Day as a holiday came to the fore in Boston, in the Massachusets Colony. They thought if you wore green, you were invisible to the Leprechauns, which was good because they pinched anyone they could see. So the pinching is to warn and remind you about the Leprechauns.
Pinching those not wearing green on St. Patrick's Day is an American tradition, having nothing really to do with Ireland or Saint Patrick.
And because nobody does it better than Martha, here's a link to a sweet Saint Patty's Day project, for those of you (like me) with way too much free time on your hands:
*This information is from Wikipedia, where all good and reliable research information is found.(actually, I just said that to irritate my sister Aimee).