When arm rests are provided they are provided for the use of both parties. Not alot of thought as to 'ownership' was given when the service was put in place. Generally, most realise or are aware that more than one can easily 'share' the rest. At the movies in Bumble Town - NZ, where I come from, there also seems to be alot of interest in sitting next to one the three one armed folk that live here. Other than those guys being good blokes, there is never a conflict over 'ownership'