What other way could the situation have been handled?

I went home to visit my father who lives 2000mi away. Since I couldn't come home for father's day, I celebrated with him by taking him out to his favorite restaurant for lunch. While I was in the bathroom washing my hands, in walks one of the waitresses and rudely asks me "what you doin here w/ that old man"! I was shocked for a minute, then I walked out and complained to the manager about what happened. I yelled it loud & clear so the staff would know he was my father, but it was none of their business anyway. I felt bad afterwards cause my dad goes there all the time, and now he feels embarred and thinks I should've brushed the matter off.