Re: not stacking bins:
I was stacking them to make some room at LHR T5 once, and the security guy down the other end starting shouting, "DO NOT STACK THE BINS. SIR, DO NOT STACK THE BINS!" I just kept my head down in a "I no speak English" manner and carried on stacking. I mean, there was a huge pile-up, things were falling off the belt, and these guys were just ignoring it.