You get creative by writing the obvious.
Seriously! Why does A hate B? Give yourself 10 minutes, to think of every obvious answer you can, and write it down. Once you've written down all the obvious answers, exclude them.
You are not allowed to use those answers. Think of something else. The next thing that comes to mind that is not one of these answers, is creative enough to use and expand upon.
Why does Jill hate Bob?
- Bob tried to rape Jill.
- Bob is rich and shows it off.
- Bob told Mike he slept with Jill, a lie.
- Bob stole something from Jill.
- Bob is ugly, and Jill is shallow, disgusted by him.
- Bob is gay, and Jill is a homophobe.
- Jill is in love with Bob, and Bob ignores her.
- Bob is great at something, and if it weren't for Bob, Jill would be #1.
- In 3rd grade Jill wore braces, and Bob told her they were ugly.
- Bob is a mixed-race child, and Jill's mother told her that was sinful.
- Bob is lazy and doesn't do his fair share of work.
- Bob is a star, and gets everything he wants without trying.
- Bob was silently crying during a war documentary in the 8th grade, and Jill thinks he's "not a real man".
- Bob brags too much, he's a loud mouth, and doesn't know what he's talking about.
I'm out of time. Those are the obvious answers, in each one "Bob" can be a completely different person. Who "Bob" is doesn't matter that much, we'll decide that after we figure out why Jill hates Bob -- That is what will define Bob.
So the next step is to think of a reason that is not any of these obvious answers, and that you could build a story around.
For me, in 10 minutes, one I did not think of is maybe Jill is actually strongly attracted to Bob, but upbringing and religion forbids her from such sinful thoughts. This has nothing to do with Bob, Jill's struggle is internal, her enemy is herself, or her parents. Her desire for Bob is forbidden, and she blames Bob for attracting her, when Bob is completely innocent, and perhaps also strongly attracted to Jill.
So, we have a love story. If I wanted to make Bob another race, or a foreigner, that might help explain Jill's conflict; her parents and church and social circle would never approve. Shades of Romeo and Juliet -- I have to decide if I want to embrace R&J or avoid it.
Of course what is obvious to you may not be obvious to me, and vice versa.
What is important is that you get rid of all your obvious answers, as fast as you can, and then exclude them. So you are forced to think of something non-obvious to you, and therefore fun to work on.