Colleague and I received boarding passes on a CAAC domestic at Beijing. This the days when boarding passes where drawn sequentially from a cardboard box. Pax one in line got 1A, number two 1B and so on.
Entering the aircraft it turned out that our seats did not exist, in their place were lavatories. Problem solved during take off run, with the two of us standing in the aisle. Amusing, and kudos to the cabin crew for not panicking (caring).
This exact same thing happened twice, both times on B737 that had an unusual lavatory location. Two-thirds aft on the port side.
Happy days flying domestically China early nineties.