What logical fallacy are most irrational?

No, your pet peeve does not count. Universal healthcare, affirmative action, "political correctness", religion, phobia, or emo kids are not logical fallacies though perhaps people arguing for it often use logical fallacies. A logical fallacy is an argument tactic, not a belief, that is irrational. For example, appeal to fear, equivocation, strawman, no true Scotsman, Texas sharp shooter, and bulverism are logical fallacies.