Yeah, Slipknot is correct. Using the term "bong" can get the owner in trouble. Why? Because if you live in a jurisdiction where sale or possession of drug paraphernalia is a crime then referring to the water pipe as a bong (a term associated with drung para.) and then selling and/or buying it has got ya in the hot seat. Some jurisdiction's statutes or ordinances actually use that exact word, "bong" as a descriptor of drug para. So now you understand why the clerk doesn't want to acknowledge the existence of a "bong" in their shop.