To get all your news from biased sources who spin news stories in such a way as to keep relevant facts away from the listeners and further an agenda. People who watch NBC or MSNBC news are the most likely people to suffer dumbassification.
Some things that can lead to being dumbassified is listening to edited soundbytes which conveniently clip off vital words, phrases, or sentences. Also, being shown doctored photographs, or strategically cropped photos that change the context of what is being shown.
Dad, you've been listening to MSNBC news for so long you've become dumbassified. You should consider listening to some "hate radio" shows like Rush Limbaugh's, Sean Hannity's, Neal Boortz', and Erick Erickson's, for a few days in an effort to shake free from your bad case of dumbassification.