I sat next to one once, it was a short flight, only a little over an hour. He acted typically enough, rested his feet on the bulkhead and rested his eyes for a few minutes, read, went to the lav, talked to the FA, talked to me, stuffed a wad of tobacco in his mouth. He was sitting in row 1, so he certainly wasn't watching over the cabin like a prison guard. I didn't notice how closely he watched during boarding.

Saw one board another flight, but as he wasn't sitting near me, I don't know how he occupied himself.