Many people are confused about what counts as a fallacy, including teachers of critical reasoning. Opponents of science often accuse pro-science writers of "the fallacy of authority" or "the ad hominem fallacy" when they are noted for having made silly and false claims before. I thought some words about what a fallacy actually is might be to the point.When marking essays, one of the most common errors I have noticed students seem to make (IMHO) is claiming something is a fallacy when it is not. For example, as soon as someone mentions the name of an authority in a particular field as a reference or a rhetorical device, students will often say it is an Appeal to Authority. E.g., when critically evaluating an essay about self esteem in which the author refers to Alfred Alder as the father of the concept of inferiority, students will somehow misconstrue (perhaps in desperation) this as an Appeal to Authority. Whereas, it is simply a legitimate reference to the history of the idea; just as when writing about evolution (say) you would often refer to Darwin, or Mendel with genetics.
In a similar vein - this post deals with someone who thinks he's found a fallacy when he hasn't.
Update: See Red Flag Faux Pas