Fifth grade.
The night before I unlocked Super Sonic in Sonic R on PC. I really wanted a reason not to go to school or come home early.
Boy did I get it.
Mom left work and picked up my older sister from middle school. Then she picked me up from school. She started walking really, really fast, which was very weird because she's really fat.
I asked whats going on and she said "America is under attack!"
I said wut and she screamed "WE'RE GOING TO WAR!!!!!"
Then she started crying and freaking out because at the time one of my cousins was in the Marines.
We came home just before or just after both towers fell.

The meme "turn on tv, it doesn't matter what channel" is true. Unless it was a channel for children like Cartoon Network, it was in EVERY channel.
I remember on Cartoon Network/Toonami it was Goku vs that Green guy in the After-Life King Kai championship.
I got to spend the day playing as Super Sonic in Sonic R on PC, so I got what I wanted.