Crazy People is a 1990 movie starring Dudley Moore as a burnt out advertising executive whose mental breakdown lands him in a psychiatric hospital. With time on his hands, the man is inspired to make up new advertisements, such as an ad for Volvo, which proclaims "Buy Volvos. They're boxy but they're good." In the sanitarium he falls in love with Kathy (Daryl Hannah), a fellow patient, and transforms the place into a branch of the advertising industry, where other mental patients come up with wild, often funny advertising slogans, like "Forget Paris. Come to Greece. We're nicer," for a Greek travel agency or "Most of our passengers get there alive" for United Airlines and “Visit New York, It’s not as filthy as you think”.

Thanks to wikipedia for help with the synopsis of the film!