Determining the rarest phobia is difficult, as comprehensive data on phobia prevalence is limited. However, some phobias are considered relatively rare. One example is Arachibutyrophobia, which involves a fear of getting peanut butter stuck to the roof of your mouth.
According to provided reference, Arachibutyrophobia is a rare phobia that involves a fear of getting peanut butter stuck to the roof of your mouth. This fear may stem from a general fear of choking or negative experiences like peanut allergies.
Therefore, while it's impossible to definitively name the rarest phobia, Arachibutyrophobia is recognized as one of the less common phobias.