I witnessed this happen. Guy boards a few people after me, looks like he hasn't slept in a day. Walks miserably to the middle 5-wide row right before mine, moves to the center seat and buries his face in his arms to get a nap, then puts them down in resignation waiting for someone to take all his elbow room.

Every single seat on that plane was full except by some miracle his row. It didn't even fully register until we were in the air. Dude looked around like he was being pranked the entire time from when the door closed until the tires left the ground. As soon as the seatbelt signs turned off he put up all the arms and laid down across all five seats. He didn't move until we landed like 12 hours later.