I just had a short haul flight with LH on a A321 and was allocated a middle seat. From my 20+ years experience as a traveler, I've always found that the passenger in the middle seat gets access to both armrests since the passengers on the aisle and window have extra space, they can lean "outwards" of the seat, while the passenger in the middle has the least shoulder space. If not full access, then occasionally access to both.

The passenger sitting next to me on the aisle seat was very tall (maybe 6'3) and was hogging the armrest. I politely (and I really mean politely) asked if he minded if I used that armrest, and he replied immediately "No.", I then said "but I'm sitting in the middle seat and it's common courtesy that I'd be the one using it", to which he replied "We can share", turned his face away and left his arm exactly where it was. I'm attaching a picture of what he called "sharing".

Since we couldn't solve this little issue, I asked the flight attendant if she could convey to him that it's common courtesy to let the middle seat passenger use both armrests, to which she replied "You two should solve it on your own, I'm sorry, but there's nothing I can do, this flight is too short for that". What did she wanted us to do, arm wrestle for it? I wouldn't even have been able to do it, that armrest was tiny.

So my question to the Lufthansa lurkers here: why so little love for the middle seat passenger? And how long does a flight have to be for common courtesy to kick in?