I'm with FlyingCruiser . I rarely sleep much on flights so on very long haul flights I will tend to stroll to the back, stretch out a bit (standing) near the rear galley & lavs and back. Never during a meal/drink service and never in a higher cabin than the one I am assigned to. Also if there are line ups for the lavs or other traffic I would refrain. Have often had some great conversations with crews too. I have worked a lot in the service industry and am a plane geek so often found kindred spirts.

Very few people tend to want to do this, so if done correctly I don't see how one or 2 people from up front would make much of a difference in the hundreds in the back and have never has a crew member indicate it was not OK.