Let me start.
I was in the car, listening to the radio. Then the regular (hourly) news broadcast came and it was told that in america an airplane flew into a building. A few weeks before that a small plane crashed into a building, with only the pilot being killed. My first though was, based on what I heard, that this was again some idiot that should never had stepped into an aircraft.
Then, during the ride home, more broadcasts came telling that it was a passagers plane. Then it was told it were two...
At home I told this to the person I lived with (I was sharing a house with a female friend at that time) and together we watched the news broadcasts for the rest of the evening on tv. She cried, I was disgusted/appalled...
Yes, I still remember this. I don't think I will ever forget.
Later that week I heard that 2 of my colleagues were in one of the planes. They did not survive it. That was a moment that also made a great impact on me.