First the new ones:
Scriptum Ergo Regula, or “written, therefore rule.” This is the fallacy that allows some to claim that every facet of the printed siddur, or any idea that occurs in a halachic work, has halachic weight. This is simply not true, and is reminiscent of what I heard, I believe in R’ Scachter’s name, in response to someone not believing the rabbi could take a particular position: “Write it in a book, then shoot me.” “Why should I shoot you?” “Because when people see a position written in a book in the name of someone dead, it suddenly becomes a halacha.”
Disimilis Ergo Malus, or “different, therefore bad.” This is the Hatham Sofer’s hadash asur min hatorah motto on steroids, and a common, normal, and unfortunate aspect of all human behavior and social interactions, and is also the source for many ills that plague Jewish religious life, like allergic Judaism and baseless hatred.
And the older ones:
The “Are You Rav Elyashiv?” Fallacy
Reductio Ad Opinionibus At Dissiderent
From Avraham Ben Yehuda, here.