Is self-infallibility a mental disorder?
I've not seen self-infallibility listed anywhere; however, there are a few psychological constructs that may be useful:

Dark Triad
DSM5 - Conduct Disorder
DSM5 - Narcissistic Personality Disorder
DSM5 - Antisocial Personality Disorder

Overconfidence may be a synonym for self-infallibility in the context you are thinking.  Overconfidence would normally be thought of as a component of narcissism.
More information would probably be required to distinguish between the four identified psychological constructs but hopefully these four links are a starting point for further research.
References
Jones, D. N., &amp; Paulhus, D. L. (2014). Introducing the Short Dark Triad (SD3): A Brief Measure of Dark Personality Traits. Assessment, 21(1), 28–41. https://doi.org/10.1177/1073191113514105