I thought Boromir was one of the best portrayed actors in the Trilogy, even if they did get some details about him wrong. I'd never heard of Boromir being called the derogatory term "Borrums" either and I don't have any plans to start calling him that. The horror! What an insult to Boromir's nobility!
But for some reason I don't have a problem calling Denethor "Denny". Oh well, I'm weird.
