"I'm a doctor, not a bricklayer!" In the original iteration of Star Trek, Dr. McCoy always had an objection to being asked to do anything other than standard medical care. By the end of the show's three-year run, it had become his catchphrase, only varying by the occupation -or object- he was not.
He's not the only doctor who is not something else. The phrase was resurrected for later Star Trek series: Deep Space Nine, Voyager, First Contact, and Enterprise. The exception was Dr. Beverley Crusher, who never turned down an opportunity to work outside her specialty. By now, you'd think Federation recruiters would specify that medical personnel need to be flexible in their duties. The catchphrase was not limited to doctors, either, although that's what we recall most often, thanks to McCoy. Memory Alpha has a list of instances in which the phrase, or something close to it, was used. It's a long list. -via Laughing Squid