It's the craziest story -- the father of 19-year-old Shawn Christy tells us it all started back in 2009 ... when his son began receiving "ominous" text messages from an unknown number.
According to Shawn's dad, the person sending the texts dropped several hints about her identity, including that she's from Alaska and works in politics ... and for some reason, Shawn believes the culprit was none other than the former governor of Alaska herself.
So why would Palin contact some random guy in Pennsylvania? Shawn's dad couldn't explain that part.
But Mr. Christy did tell us they alerted the FBI -- which didn't investigate Sarah, and instead turned on Shawn ... gathering evidence against him to secure a restraining order.
Shawn's dad tells us they've spent thousands fighting the protective order to no avail -- and have since been forced to declare bankruptcy.