As a kid growing up we were always told we would be pinched on St. Patrick's Day if we didn't wear green. So, I was curious to find out why. There are two versions of the story according to stpatty.info. One version is:
Pinching is thought to had started in American classrooms. It is strictly an American obsession. Kids were also a major driving force behind wearing green during the holiday. The school children would pinch anyone who did not wear green. Reason for this seems to be that the early Irish immigrants to the U.S. (after the Potato Famine) were oppressed and not welcomed with tolerance’s warm embrace. The Irish were thought of as drunkards. Many businesses had ‘Irish need not apply” or simply “No Irish!” signs in their windows. When the holiday became more mainstream with their arrival to the U.S., the adults would pinch anyone who was Irish that did not wear green for lack of pride and respect for their heritage. The color being symbolic of the proud Irish rebels who stand up to the English occupants that persecute them. It was at this time that the shamrock evolved into a political statement of Irish nationalism. Children took pinching a step further and pinched anyone who did not wear green.
The other version is...
Pinching those not wearing green on St. Patrick’s Day is an American tradition, having really nothing to do with Ireland or St. Patrick. It’s thought that the pinching started in the early 1700s, about the time that awareness of St. Patrick’s as a holiday came to the fore, too, in Boston, in the Massachusetts colony. They thought if you wore green, it made you invisible to the Leprechauns, which was good because they would pinch anyone they could see. So the pinching is to warn and remind you about the Leprechauns.
Although less likely to be true, I personally like the second version.
Happy St. Patrick's Day!