Pain resistance mechanism
A pain resistance mechanism is when someone gets so used to being messed with that new pain just feels like a Sunday morning. They've been through the ringer and are ready to ignore anything new.
After getting stood up ten times, she showed up to a wedding and just ate cake.
He got rejected by every girl in school, now he just walks into fights with a smile.
She had her dog stolen, her house broken into, and now she's just mad at the neighbor.