Ah ha ha. Can't resist quoting at length from Terry Pratchett, who has the definitive word on this phenomenon. This is from "The Light Fantastic", abbreviated a bit:

"The Forest of Skund was the only forest in the whole universe to be called, in the local language, Your Finger You Fool, which was the literal meaning of the word Skund.
"The reason for this is regrettably all too common. When the first explorers travelled into the chilly hinterland they filled in the blank spaces on their maps by grabbing the nearest native, pointing at some distant landmark, speaking very clearly in a loud voice, and writing down whatever the bemused man told them.
"Thus were immortalised such geographical oddities as Just A Mountain, I Don't Know, What?, and of course, Your Finger You Fool.
"Rainclouds clustered around the heights of Mount Oolskunrahod ("Who Is This Fool Who Does Not Know What A Mountain Is") as the..."