If you "have it in" for someone, you have animosity towards them. You are against whatever they do or say just because you don't like them.
An idiom is a saying or expression. There are many idioms that mean to stay away from, or avoid, someone. An example of such an idiom would be, "to steer clear of" someone.
save someone's life
To openly discuss a disagreement with someone.
This is supposed to mean that someone is talking about you.
The idiom "crack someone up" means to make someone laugh or amuse them greatly.
This is not an idiom. It means exactly what it says -- someone is putting their hands into their pockets.
Keep bothering someone.
it means to control someone
To blame someone else for an error.
It means someone has blue eyes.
It's not an idiom. "Cool" is a slang term meaning someone is popular or fashionable.
It's not an idiom because you can figure it out. It's a childish rhyme meaning someone who is not pretty.