The only time I was turned down when asking for the entire can was on a flight from MCO to EWR with DL. It was years ago. "We only serve glasses of soft drinks on this flight." I had already asked for "no ice" and when she gave me the cup of soda with ice, I just took it and wasn't going to say anything. But my Dad who was flying with me was insistent so he mentioned to the FA that I asked for no ice. She ended up throwing the cup away with the soda with ice and gave me another glass without ice. Funny, because she ended up using about a full can on me anyway!