Final answer:
The horn should only be honked to alert others of your presence for safety reasons, such as preventing accidents or warning of imminent danger.
Step-by-step explanation:
The only phrase a horn should be honked to say is to alert others of your presence on the road, specifically for safety reasons. Using your horn should be limited to situations where you need to inform other road users or pedestrians of imminent danger, or when it is necessary to avoid accidents.
For example, honking can be used if a driver does not see you and is about to change lanes into your vehicle, or when someone is walking into the street without noticing oncoming traffic. It's important to note that honking out of frustration or to communicate anger is generally discouraged and can sometimes be illegal.