What part of your body do you bump into things most often?

My mom is 160cm tall, and she made me hang shelves and cabinets around the apartment at her height, which is about waist-level for me.

That's a bit strange. If you're 186cm tall and your mom is 160cm, you should just be able to ignore the cabinets. How could they possibly hit you in the forehead?

For example, my mom is 165cm tall, and I'm almost two heads taller than her – and I have no problems with the cabinets.