Fallacy: Two Wrongs Make a Right

Here are some examples I could find in my social life:

1. I have borrowed amir's expensive pen, but found I didn't return it. He tell's himself that it is okay to keep it, since I would have taken his.


2. After leaving a store, Maryam notices that she has underpaid by $10. She decides not to return the money to the store because if she had overpaid, they would not have returned the money.


3. 
   Amir is horrified by the way the state uses capital punishment. I said that capital punishment is fine, since both of us don't have any qualms about killing others.