借过一下。

You say this while you are moving. Don't wait until you are stuck for five minutes. Say it clearly as you approach the person blocking you. Most people will instinctively step aside. You can add a small nod to show extra politeness. It is like a social lubricant for busy sidewalks.

Use it whenever there is a physical barrier made of people. It is perfect for getting off a crowded subway train. Use it at a busy night market while holding oily snacks. It works great in a narrow office hallway. If you are at a concert and need the bathroom, this is your best friend. It saves you from awkward shoulder-tapping.

Do not use this to get someone's attention for a question. If you want to ask for directions, use 请问. Do not use it if you bumped into someone already. If you stepped on a foot, say 对不起 instead. It is for "passing through," not for apologizing for a mistake. Using it after a collision feels a bit like saying "Get out of my way" retrospectively.

Chinese culture values social harmony in tight spaces. In mega-cities like Shanghai or Beijing, personal space is a luxury. 借过一下 acknowledges the other person's right to be there. You aren't demanding they move; you are "borrowing" their space. It reflects a culture that is used to high-density living. It turns a potential annoyance into a polite transaction.

You can shorten it to 借过 if you are in a huge rush. Adding 麻烦 (trouble) at the start makes it even more polite: 麻烦借过一下. If you want to be super formal, you can say 请让一下. However, for 90% of your life, the standard version is perfect. It is the "Goldilocks" of polite navigation phrases.