I'm going to deny my ex friend even a penny for his dad's birthday
Why would you refuse everything?
I think it's reasonable to never remember his dad's birthday.
Even if you aren't getting along you should still help them out. Its only right to treat people nicely and give to those who need help.  After all, his father did nothing wrong to you.
Ha, as long as they don't need help I'm fine not treating them nicely.
I still think that you should help out. If your friend needs it, I think that it is reasonable and kind to want to help.