The more you try, the worse it gets. Just accept that you hate
him. Just also know that sooner or later, the hate will go
away.
If you hate him and is not doing anything about it, then there is
no problem right? It is all in your own head?
The other way is to examine why you hate him and whether it is
justifiable to hate him to that extent. What did he do to make you
hate him so?
Your head cannot be thinking of two things at a time. You cannot
hate when you are thinking about some thing else. So everytime you
think of him, force yourself to think of something else.
Better still, channel the hate into something positive. Hate can
generate a lot of energy. Channel that energy into something
positive.