What makes a crank

Unified theory of the crank: Denialism Blog
Here at denialism blog, we're very interested in what makes people cranks. Not only how one defines crankish behavior, but literally how people develop unreasonable attitudes about the world in the face of evidence to the contrary. Our definition of a crank, loosely, is a person who has unreasonable ideas about established science or facts that will not relent in defending their own, often laughable, version of the truth. Central to the crank is the "overvalued idea". That is some idea they've incorporated into their world view that they will not relinquish for any reason.
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Wikipedia has an excellent wiki on cranks; I find their criteria are more modern:
1. Cranks overestimate their own knowledge and ability, and underestimate that of acknowledged experts.
2. Cranks insist that their alleged discoveries are urgently important.
3. Cranks rarely if ever acknowledge any error, no matter how trivial.
4. Cranks love to talk about their own beliefs, often in inappropriate social situations, but they tend to be bad listeners, and often appear to be uninterested in anyone else's experience or opinions.

In addition, many cranks:
1. seriously misunderstand the mainstream opinion to which they believe that they are objecting,
2. stress that they have been working out their ideas for many decades, and claim that this fact alone entails that their belief cannot be dismissed as resting upon some simple error,
3. compare themselves with Galileo or Copernicus (or in a religious context, Noah), implying that the mere unpopularity of some belief is in itself evidence of plausibility,
4. claim that their ideas are being suppressed, typically by secret intelligence organizations, mainstream science, powerful business interests, or other groups which, they allege, are terrified by the possibility of their revolutionary insights becoming widely known

Crank Magnetism: Denialism Blog
Back when we wrote the Unified Theory of the Crank one of the main things we discussed related to crankery is their inability to recognize competence in others. As a result, cranks tend not to mind the crankery of others, since they see themselves as opposed to a scientific orthodoxy. Consistency be damned, they just want to see science with egg on its face so they can prove that they are being persecuted.