Insider asked a group of people who used to work at fast-food chains about some of the frustrating things they wish customers would stop doing.

Not knowing what you want before ordering can hold up an entire line.

Using the bathroom without buying something is often considered rude.

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Fast-food restaurants are convenient for grabbing a quick bite, but there are certain behaviors you may want to avoid the next time you pick up some fries.

Insider spoke with a group of people who used to work at fast-food chains to figure out some of the most frustrating customer behaviors and habits.

Here are eight things you should never do in a fast-food restaurant.