I remember it vividly. I was watching when the second plane flew into the World Trade Center. They'd just shown a close up of where the first plane had gone in. Having been there before, I knew it had to be a passenger jet due to the size.
When the second one went in, I turned to my wife at the time and said, "We're under attack."
I had the day off and stayed glued to the TV the rest of the day.