Clinic Doctor was the doctor in the clinic at St. Sebastian's Hospital who saw Gregory House when Cuddy cut off House's Vicodin in the Season 3 episode Merry Little Christmas.
House was trying to get a doctor to give him a prescription for Vicodin. He posed as a patient who had been in an automobile accident and had suffered a facial fracture. These are very painful, but are easy to fake as they are difficult to detect and often heal very slowly.
The doctor first offered House gabapentin, but House claimed it made him nauseous. The doctor then offered him acetaminophen with codeine. House was more receptive this time, but then claimed he had not slept in days. The doctor admitted codeine wouldn't help him sleep, but Vicodin would. House thanked him, but the doctor then said they couldn't give narcotics to new patients to discourage drug seeking behavior. House asked if the doctor thought he was a drug seeker, and when the doctor said no, House tried to talk him into writing the prescription. The doctor held firm to policy. House lost his temper and noted gabapentin would be useless for broken bone pain as it only affects nerve pain. The other doctor realized House was a doctor too and went to call security. Instead, House insulted his abilities as a doctor and stormed out.