I hate the girl I dated for the past four months.
Why would you date her if you hate her?
she was always late for dates and complained about how I'm a bad boyfriend.
It sounds like you're moving on. It's not healthy to hate someone. Having such hate can tear you down emotionally.
It feels great to hate...
If the relationship is making you feel that bad, why don't you just end it. It is not okay to hate people, so ending the relationship seems like a good call.