I am generally not one to judge one's fandom, but I'm not exactly feeling it with this guy. Someone down in San Diego spotted this guy at the San Diego Chargers-Oakland Raiders Week 7 matchup. He is sporting a 49ers tattoo and some Raiders gear.
I've seen people that will sport the split A's-Giants baseball cap from the 1989 World Series, but I still can't figure out the split fandom. I don't hate the Raiders, and do prefer they win when it is not against the 49ers. But that is different than rolling out in Raiders gear with a 49ers tattoo.