Also spelled Gris Gris - A False and/or sometimes idiosyncratic or ridiculous belief that lay in someone's blind spot. An Irrational view which is inconsistent with their general outlook.
The term originally comes from an African Charm that is worn to ward off evil and even as contraception and was mentioned on Penn and Tellers show called Bullshit as being in common usage among their staff.
"That dude is pretty reasonable mostly, but he totally believes in astrology."
"Yep, Everyone's got a gri-gri. "