There's no reason for a store to tell you what to do with something after you pay for it. It's coffee, not a gun. It's a refreshment, not a prescription. He's buying, not renting. If he wants to take it into their restroom, pee in it then swill it down, it's none of their business. They should have given him a cup of ice with his coffee, explained to him that what he was asking them to do went against the sacred rules of their cult, patted him on the shoulder and helped the next infidel in line.

I loved Harry Anderson's take on this theme, "Games you can't lose: A guide for suckers".
Link to Amazon page: http://tinyurl.com/2luavy