When he says something you vehemently disagree with, one technique is to simply reply: "You're certainly entitled to your own opinions; however, you're not entitled to your own facts." Then continue with whatever you were doing as if you had him on ignore. After hearing that reply, repeatedly, most people will realize that just standing on a soapbox doesn't cut it anymore. Don't argue with him: wait until the bravado tones down and he's willing to discuss the issues. Keep in mind that he may find your recently acquired scholastic knowledge intimidating; so, accentuate the gist rather than the source.
