Invade our personal space.
Sitting with 4 people in a row of public transport seats which would fit a maximum of 2 people back home or standing in a huge bulk not in a proper queue are situations which make us extremely uncomfortable. The same thing goes for traffic. When we can’t see your registration plate in the rear view mirror, you are too close. When we can feel the warmth of your skin or smell in your breath what you had for lunch, you are too close. It’s nothing personal. We Germans just like to be alone in our own personal space bubble and we don’t really know how to handle it when someone invades it, except with either retreating really quickly or becoming stiffer than a broom.