The User is Drunk is a product and UX design principle that looks to make products so intuitive even someone drunk on alcohol could use them. Additionally, developers can use it in the context of site testing by asking someone drunk to try it.
This principle began when UX designer and developer Richard Littauer came up with the idea and offered the service on his website TheUserIsDrunk.com. It soon became a huge success. So much so that he was inundated with offers to test websites.
Of course, there is something comic and tongue-in-cheek about this method. However, it does shine a light on a healthy attitude towards design.
Firstly, it encourages developers to keep things clean and uncluttered. Because developers are deeply familiar with their product, navigating it is easy for them. But The User is Drunk mindset forces them to consider the experience of someone using the app for the first time.
Secondly, as Littauer makes clear, many users use applications or software in a distracted state. UX teams often design products based on having 100% of the user's focus. In reality, this is rarely the case.