Are you immune to the effects of caffeine?

I love coffee but I have never experienced a “caffeine buzz” and assumed I was immune to it. My friend said I was just addicted. I proved him wrong by completely stopping any caffeine intake for 2 months, and experienced no ill effects or withdrawl symptoms. Then I went back onto coffee again and still had no effect. So now I’m even more convinced. I also cannot tell the difference between ordinary coffee and decaf. Am I alone or does anyone else experience this?