True Story: An employee comes into my office for the sole purpose of saying goodbye for the evening, and puts a bottle (2/3 full) of apple juice on my desk. He says, "I just added a bit of this to my glass of water today - I didn't drink from it. You can have it." The container has what looks all the world to be like apple juice.
The words, "Do Not Consume If the Seal Has Been Broken" readily spring to mind. It's a good philosophy and has served me well in the past.