The power of NO!

I told the General Manager "No" and he did not take it so well!
Few years ago, GM called me to his office asking for a technical help.
It was my first weeks in the job~
After I finished, he kindly asked me to grant him an admin access to the system!
I refused I told him it is confidential!
He insisted for a bit claiming he has a great relationship with my direct manager who will never say no to him~ I told him: “Cool, call him now and let me see”.
He got angry and shouted: You are new employee here and I am the GM! Give me the access! I told him: No I can't I am sorry & I left.
I reported this immediately to my manager and he was happy~
Few minutes later I saw GM is leaving my manager’s office angry without looking at me~