That's one of those weird unwritten rules where the seats recline, but no-one wants you to actually recline your seat. They should just remove option from all seats, if the person behind you is gonna get ticked every time you recline your seat.
I agree, nobody actually wants anyone to recline at all. But....should be common sense *not* to recline when meal service is taking place. The other thing that always happens when seats in coach are reclined....someone inevitably has a hard time getting out of their row to use the rest room and holds onto the top of seats in front of them.