To be honest, I grew up in a diverse city with a diverse group of friends, race didn't matter all that much to us. I guess as kids, we didn't see what was out there. We were certainly aware, and I was given speeches as a kid about understanding that I'd have to be undeniably better to be seen as the same but it wasn't immediate to me. No one ever had the gall to directly say something racist to me to my face, there were certain actions sure, but even my friends who were of other races told them that they were ignorant. I remember a game like SOCOM US Navy Seals being the first time I heard someone use the n-word in a derogatory fashion in real life. It just didn't happen, and maybe we were fortunate.
I'd say the internet makes me think more about race or religion or any of those things than I do normally. That's not to say we didn't know racist people, we had friends whose parents didn't like black people (grandparents especially), but we always chalked it up to an older era. I'd seen enough to know my friends didn't think that way, and to this day, a lot of those people would ride for me before my black friends would. Though not as egregious, my older relatives had habits like calling every Asian person Chinese anyhow so I couldn't exactly be to upset by a little ignorance. We were special.
It wasn't until college that I found out how rare my experience was, and that most people lived self-segregated. Class, race, religion, none of that stuff had ever mattered to us. It's why when I see any sort of generalization in here I

because I know that's not how real life is and we've all branched out to other parts of the country and the world and found out that we weren't all that unique. People have more in common than was separates them if you give them a chance. I think I got a bit off-topic there.
But to answer the question when it really hit me what being black in america meant: It was during the uproar of Cornel Young Jr. being shot and knowing his little sister. If anyone remembers that case.