I have a feeling whenever my friend is at work they seem different.
What do you mean that your friend is different?
They're becoming a more and more negative and hateful person.
If your friend at work is becoming more negative and hateful, you should talk with your friend and find out what is bothering him or her. If you can support your friend and help him or her address the problem bothering them, they will become less negative and hateful and back to their regular self.
I want my friend to be the same at work and home. If they are not negative and hateful at work, then they can be a better person.
I agree, not bringing that negativity in the workplace would be a good thing. I definitely recommend having a one-on-one conversation with him to see why they are acting the way they are.