The phrase "visitor from a different planet" is a common way to describe someone who is unfamiliar with the customs and culture of a particular place. However, there are many different synonyms that can be used to describe this concept. For example, one might refer to this person as an outsider, a newcomer, or a foreigner. Similarly, terms like extraterrestrial, alien, and martian could all be used to describe someone who is not from Earth. Ultimately, the choice of words will depend on the context in which they are being used, as well as the tone and intent of the speaker or writer.