People who get upset about spoilers are some of the lamest people around. Knowing details about a good story doesn't devalue its quality and crying out when someone talks about it only serves to stifle discussion. Using spoiler tags and other methods does nothing because people will click and look at them out of curiosity anyway.
I won't purposely spoil plot details for no reason, but if people are discussing it I think it's silly to keep quiet just because someone hasn't seen it yet.