Glamgirl, thanks for the lecture on your airlines UM policy. I do understand the reasoning behind it. My actual question related to it being an unwritten rule.
If your airline SOP's STATE in BLACK AND WHITE that UMs cannot be placed next to a MALE then your insinuating that ALL MALE passengers are sexual predators. Which is wrong. Leaving yourselves OPEN to many legal/court cases.
Search BA, QANTAS etc and other such non 'amatuer' airlines under constroversies. Its interesting reading.
Many airlines have unwritten rules, both amatuer operations and non ameatuer operations - as you refer to them.