Just sit where you like - it works for some it seems....
I had the pleasure of flying from London to Jeddah the other day. There were at least 40 people in our cabin in the wrong seats, one of the party had all the boarding card stubs. After about 20 minutes of argy bargy the cabin crew gave up and left everyone to it.
Coming back, the same situation - my seat was within a family group all of whom were seated together (none in their allocated seats). This time I gave up asking for my allocated seat and went aft to an almost empty cabin and a choice of rows to myself.