Usually early in a flight, and once it's established that there are some empty seats - that is, occupying an empty one rather than asking someone to switch. Alt

Usually early in a flight, and once it's established that there are some empty seats - that is, occupying an empty one rather than asking someone to switch. Although I once got on a 12-hour red eye flight that was full, settled in and, before takeoff, had a girl a few rows in front of me come back and politely ask the man next to me if he'd switch seats with her. She didn't like the company up there, I guess. He agreed, and she and I ended up hitting it off and sharing a hotel room at our destination. Which is admittedly a rather one-off situation... I've also had the opposite situation, where I was desperate to switch but couldn't. The worst case was when I got the last seat on a flight and found myself between this completely asshole older couple where, it came out, the man would only fly in a window seat and his wife would only sit on the aisle. They bickered at each other over me for 3 hours as if I wasn't even there, and both refused to switch with me, going so far as to claim they both got airsick if they sat in a middle seat. Obviously, it wasn't even worth asking anyone else on the plane to switch, but I've never wanted to kill anyone as much.