Found this on another forum I frequent - 'cretin' is cognate with 'Christian'! I kid you not. Now if that isn't unusual etymology, I don't know what is. I quote from my friend's post:

"Cretin" derives from the French which derives from the Latin Christianus a word loosely defined as someone who's stairs don't go all the way to the top. Christianus, of course, is related to the Greek XRISTOS, "annointed one", a translation of the Hebrew MASHIACH (commonly rendered in English as "messiah").

cheer

the sunshine warrior

cretin

SYLLABICATION: cre·tin
PRONUNCIATION: krtn
NOUN: 1. A person afflicted with cretinism. 2. Slang An idiot.
ETYMOLOGY: French crétin, from French dialectal, deformed and mentally retarded person found in certain Alpine valleys, from Vulgar Latin *christinus, Christian, human being, poor fellow, from Latin Chrstinus, Christian. See Christian.
OTHER FORMS: cretin·oid (-oid) —ADJECTIVE
cretin·ous (-s) —ADJECTIVE

As noted in another thread, a deficiency of iodine in Alpine soils caused by leaching of the compounds of the element from the soils, in pregnant womens diet, results in incomplete development of brain of infant. They are to be pitied. Iodized salt can prevent it. Or availability of seafood. An anomaly to call them "Christians" since they can have no comprehension of religion. And not only Christians should feel pity for them.

Although I have no proof, the use of cretin, meaning christian, would likely be a shortening of something like "child of God", in the sense of a "simple" - or intellectually-challenged person. If this is the case, the relationship would seem rather obvious, since the Christian god seems to get both the blame for the bad and the credit for the good ...