While in the forward galley. I've had flight crew politely/subtly indicate to cabin crew to put themselves between me and the door to the flight deck when one has returned from getting a snack etc, which is clearly to try and create an impediment to me deciding to rush the flight deck when they opened the door to access it themselves.

It's not an unreasonable precaution, and however effective one may or may not believe it to be, if it makes them feel more comfortable fair enough.