While I don't OPEN carry inside Costco, I always do when I am pumping my gas. Lot's of hostile stares from our Canadian visitors (we are closest Costco over the border near Vancouver), put the only comment was an "atta boy" from the Costco gas attendant.
so boomboy007, perhaps you have missed this forum’s discussions regarding abiding by private property rights as well as COSTCO’s membership provisions which specifically ban firearms, OC or CC on their property?
Perhaps the sour looks are those COSTCO members showing distain at someone flagrantly ignoring the organization’s policies!