Nick Riviera
Wikisimpsons - The Simpsons Wiki
Summary
Dr. Nick Riviera, refered to as Dr. Nick by most characters, is some form of medical professional, but clearly lacks the knowledge and ability to be an actual doctor.
Looking through a book at the library, he saw an unltrasound of a woman's abdomen and commented that "That woman swallowed a baby!" He also gave himself laughing gas instead of Homer when performing surgery.
However, all the people in Springfield know him and when her enters, he infamously says "Hi everybody!" in a perky, upbeat tone to which everyone else in the room answers "Hi doctor Nick!" in an also perky and upbeat tone.
