Appeal to Authority/Playing With

Basic Trope: A fallacy wherein someone with questionable credentials is cited as an expert.
 * Straight: Bob, a dentist, is called in as a "medical expert" in a trial.
 * Exaggerated: Bob, the world's leading expert on dental cavities, second to none, is called in as a "medical expert" in a trial and asked to analyse the foot bones of the victim.
 * Justified: Bob does know medicine to a respectable degree, just not to the degree that makes him an expert.
 * Inverted: Bob, a doctor with years of experience, isn't allowed to testify as an expert in a trial.
 * Subverted: Someone tries to call in Bob as a medical expert at a trial. When it's revealed he's a dentist, the other lawyer asks the judge to refuse to allow it.
 * Double Subverted: However, the judge refuses on the grounds that a dentist's credentials allows him to comment on medical procedure, so the dentist is a necessary expert.
 * Parodied: Bob, an Almighty Janitor at a hospital, is allowed to testify as a medical expert because he's top of his game in janitor work. When challenged, the judge shrugs and says "he probably heard some medical jargon at some point, as well."
 * Deconstructed: People listen to Bob when they really shouldn't; as a result, either an innocent man is imprisoned or a guilty man goes free.
 * Reconstructed:
 * Aware of his lack of real expertise, Bob is very careful with what he says; he isn't as useful as a real medical expert would be, but at least he avoids saying anything totally wrong and causing justice to miscarry.
 * Alternatively, once Bob points out the flaw to the judges, they revise the rules on expert testimony so that only relevant experts are allowed in the future.
 * Zig Zagged: Bob the dentist is called in as a medical expert; the other side asks that it be disallowed, but then it turns out that the case revolves around teeth. However, the teeth are revealed not to be human teeth at all, but animal teeth. Fortunately, Bob was secretly a veterinary dentist all along.
 * Averted:
 * Bob is not allowed as an expert.
 * An actual expert is called in.
 * Enforced: The Moral Guardians of the day want people to respect authority no matter where it comes from, so all authority figures are to be treated as experts in everything.
 * Lampshaded: A bystander said: "Wait, he's testifying as an expert? What?"
 * Invoked: Aware that his practical experience will be ignored if he doesn't have a title to show for it, Bob claims to have a doctorate in some made-up field, so that people will listen to him.
 * Defied: The judge said: "I'm not going to allow Bob to testify as an expert."
 * Discussed: Commentators in the courtroom talk about Bob's credentials and argue with each other over why he's suitable.
 * Conversed: A character, watching a court case on TV, tells his friend that "they always bring in the dentist because he's a respected authority on dentistry, but they don't realise that doesn't make him a good expert on medicine".

Our doctor of tropology suggests you back to Appeal to Authority.