See also: when entering a crowded bus, tram, subway or train, you do not say a single word. You look for an empty bench. If there are none, you will have a neighbour. You stop at an empty spot and mumble something like “tschulli-ng” or “s-nch-frei?” to the person occupying the other spot on the bench. You nod in an upward direction. They reply a mumbled “türlich” while vaguely looking somewhere near your face and moving their bag if neccessary. You sit down, nod gratefully, and keep your mouth shut for the rest of the ride. Neither of you wanted this. You wanted freedom. Don’t bother each other.
If an entire bench in front of you becomes available at the next stop, though, it is not the polite thing to free your neighbour and yourself up. No, you stay right where you are. The silent stranger next to you is your silent stranger now.