CRM!
Whilst sitting as an ex-RAF jet qualified passenger at a certain American airport in a B737, the captain had just announced his intention to start the engines. At the same time I saw the wind blow a large (probably two by two metre) polythene sheet which had come loose from an adjacent stack of pallets and head straight for the No2 engine intake. I immediately pointed this out to the CC member and advised her to tell the cockpit crew. Instead she made a point of patronising me, telling me that it wasn't an issue and that everything was absolutely normal. Thankfully, it didn't go through the engine, but it could easily have done so, or caused a hot start
On another civilian flight, an RAF colleague and I watched what originally appeared to be a minor oil leak from the number two engine (of another B737) as we flew across the North Sea. The amount of oil suddenly increased until it was streaming out! We soon decided to point this out to the CC. Again, we were patronised and told everything was perfectly normal "They all do that, Sirs!"......("Oh no they don't!"). Our message was not passed to the cockpit.
We were booked on precisely the same airframe for the return flight. It was cancelled because it went tech. We made inquiries why, using the old boys' network. No need to guess which engine had a problem!