There are two major beers in Slovenia: Lasko and Union. Loyalty to the beers is often compared to loyalty to a baseball team in the US- people take it seriously. If you like Lasko and say it in a Union pub, you can expect a response similar to expressing your enthusiasm for the Giants in Oakland.
Union apparently has a more full, balanced flavor, while Lasko is lighter, more thirst quenching, and contains more hops. The interesting thing is that despite the major followings behind both beers, they’re owned by the same company. Why they would manufacture such diehard loyalty should be pretty obvious- competition is great for your market, and even better when you profit from whichever good in the market is doing best. You can read all about how the two beers are related.