Two wrongs make a right is a commonly used abbreviation for the belief that, if one wrong is committed, a second wrong will cancel it out.
Commonly used to excuse capital punishment: execution is okay because a murderer is being killed.
(Which, by presupposing that "execution" is a wrong, provides a splendid example of the logical fallacy known as "Begging the Question.")
A better statement would be this:
Given that killing is accepted to be usually wrong:
Killing as a punishment is acceptable if the criminal is a killer.
This fallacy is often committed by children. An example:
Parent: Jim, why did you pull your sister's hair? Don't you know that's wrong?
Jim: I know, but she pinched me first.