Dunno if this will help.
I grew up as a Catholic in a little country town. Due to family brainwashing I just always quietly believed Catholics were better than people of other religions. We were certainly more interesting - incense, proper warlike hymns, priests with Irish accents who drank, mysterious practices like confession and communion, lots of dressing up, AND we outbred everyone so our influence was on the rise. I was NEVER bullied about being a left footer. Other kids who were Catholics and probably brighter than I was WERE bullied, because they lacked my inscrutable smuggery.
I find being a Dockers supporter is very like being Catholic. I firmly believe we are nicer and more interesting and fairer and better in every way. This means I can just say "Yeah Right" in a very annoying tone to my Eagles friends if they are silly enough to try engage in what they think is repartee. They have learned not to go on with it.
So my pretty dodgy advice is to explain to your son why we are secretly better in every way (we have man buns, the tallest player, Brady Grey etc etc), teach him how to use the Yeah Right technique and (at the age of six) give him a few ways he can change the subject to eg PLAYING footy.