I'm not going to instantly stop being upset after my wife says terrible things
What terrible things does your wife say that can make you feel instantly upset?
She uses words like "You are so stupid!" and "I hate you!".
Being told such terrible things is very upsetting to anyone, and rude to be doing that. You have a right to be angry with it, it is not acceptable. Talk things out with her and make her understand that this is not the way to live together in harmony.
I know! But she keeps saying its not a big deal.
I hope you can tell her how it makes you feel, you don't deserve to be treated that way. There are things like couples therapy if you think you might want to save your relationship I can recommend.