Just so you are fully informed, the person whose account you are planning to use will receive a notification that there was a new login to their Netflix account; the notification will give information as to the city and the type of device that was utilized.

(Obviously this would not be problem if the person is aware that you want to use their account.)

For example, with our family's Netflix account, I have received notifications of a new login from an unfamiliar place, and I determined that it was likely a buddy of one of my children - they likely remembered the login and password after they saw one of my kids input it.