I wanted to know how do you create a sim to hate each other?

When they first interact, have them slap each other, brag, that sort of thing, and continue to do that...

Talk to the sim u want to hate when all your mood bars are down low.
He will be cranky and the other sim won't like it.
And what chihuahua momma said 2.

Agreed with both these things.

Also if you have an expansion pack then you can make sims furious with each other by having them sleep with eachothers parteners etc.

Or you enter the commonly used cheat "boolproptestingcheatsenabled true" into the cheats box whilst playing with the family with the people you want to hate each other. Then exit out the family, go back in, find the relationship bar of the sim you want it to hate (on the relationships panel) and you can drag the bars right down into the red zone to -100!