I just flew back from London. as the flight near New York City a disheveled middle eastern looking man started pacing up and down the aisle. He did that all the way to Atlanta. Could be his legs were tired or maybe he was just messing with us. But my sense is that people are watching this crap and on the ready.
I had the same thing happen to me on a trip back from Cozumel to Dallas. A man from Lebanon was sitting right next to me and my girlfriend. He was in the aisle seat. Soon after take off he began pacing the aisles, then got back in his seat and placed his head between his legs like he was praying. Then got back up and started looking out the emergency exit doors, just freaking everybody out.
I told the s.o.b. he needed to sit down because he was making EVERYBODY on the plane nervous. He made some excuse about being afraid to fly over the ocean and such. He was also asking questions like "are we over Texas yet? or "are we over the U.S. yet?" just scaring the crap out of us.
Finally, once we landed and came to a stop, he literally bolted as fast as he could to get to the front of the plane, pushing people aside, etc.
Customs grabbed his sorry ass and detained him. I called the the next day and the airline told me he was still in custody but would not release any more info.
This was all 2 months after 9/11. Scariest flight I ever took.