An upside-down cross is actually considered extremely holy, as it is the symbol of Saint Peter, who was crucified upside-down at his own request because he did not feel worthy enough to be crucified in the same way as Christ. An upside-down crucifix is considered Satanic. The difference is that a crucifix has a depiction of Jesus on it. I would wager money that 99% of people who wear upside-down crosses don’t know this.
(Source: thisishangingrockcomics, via exploding-zombies)