Any particular reason for hate ? How would you feel if your dad told you he hated your boyfriend ? Be tolerant unless you have some valid reason to hate.
Well unless it really really bothers you...you should not. Sometimes it's difficult for us as children to understand that what it means to have a partner for our parents.
If it's the worst thing you have in your life, you should tell him how it affects..but choose a right time and make sure you are rational about it rather than emotional...and do give your dad a suggestion as how he can ensure that you and his G.F have minimal interaction.
"hey dad you know that cuunt you're currently dating to try and forget mom well I don't really care for her company and therefore wish for you to dump you thank you for being a reasonable adult during these trying times in our lives" that's what you should say
Just tell him you don't care for her. Try to say it as nice as you can and realize he might get defensive. Just tell him you want him to be happy and all but you aren't on the same page as his girlfriend and for whatever reason you think he can do better.
He already knows.
Send him a txt message.
Just like that, explain why and spend time alone with your dad without her.