What is Tear A Spare?
1.
A euphemism for "to tear someone a new asshole" — that is, to come down on someone very harshly as a punishment
Okay, okay... no need to tear a spare.
OR:
Before: Don't forget to take the trash out, or I'll tear you a spare.
After: Jeez, I forget to take the trash out one time and you tear me a spare...?
See