I'm not going to pay the parking ticket from when I borrowed my friend's car.
Why won't you pay for the ticket if you were driving?
It's not my car so I don't care.
It's completely irresponsible for you to get a parking ticket with your friend's car and then not pay it. If you don't pay the ticket then your friend will be forced to pay it or he could get into serious trouble.
I don't care, he should be glad that I returned his car and never come to me with this problem again.
You are responsible for your actions while using his car and you should pay for the ticket. If you ever want people to loan you things again, you need to do the right thing.