I wish I could forget my dad's birthday every year
Why do you want to forget his birthday?
Just because I can, and to get back at him for not caring about me at all I guess
It can be hard to feel happy for his birthday if he wasn't always there for you. You shouldn't feel that you need to be glad about the occasion, but you should at least remember the date.
It's fine. I'm going to forget his birthday and listen to my mother tell me how awful I am every year.
You are aware that forgetting your dad's birthday will cause your mother grief as well, and I hope that isn't your intention. Perhaps your mother also didn't give you the care you needed, but deliberately forgetting birthdays is just worsening the situation. You should just be polite and civil, even if you don't make a big deal over birthdays.