Just because New England hasn't won the AFC Championship Game yet doesn't mean you can't buy Patriots conference championship t-shirts. Despite the fact that the Patriots-Broncos game hasn't been played yet, a sports store in New York City is already selling shirts that proclaim the Patriots as AFC champions.
Selling the shirts really isn't a huge mistake. If the NFL contacts the owner of the store, all the owner has to do is pull the shirts off the rack. A huge mistake would be getting a tattoo that says your team has already won Super Bowl XLVIII because if your team doesn't win Super Bowl XLVIII, then you're kind of stuck with the tattoo.