A few years ago I was in the last row of coach on a DL 757 taxiing out for takeoff from SEA. As we took the runway, some numbskull about 15 rows ahead of us unbuckled, stood up and ambled toward the back. The FAs in the jumpseats weren't watching the cabin and didn't see the guy until he loomed up in front of them and said, "Hey, hi. I got a lot of friends who are flight attendants..." He was drowned out by the 757's engines spooling up as we started the takeoff roll, and by the FAs screaming at him to "Lie down! LIE DOWN on the FLOOR!" Lie DOWN, dammit!" He did as he was told and said later he'd just "flaked" and forgotten we were in takeoff mode.