In spanish: Botellón. A lot of spanish people like to get drunk in large groups of people in the streets (actually not too bad idea). Bringing your own drinks is cheap and it is fun too. Unfortunately they overdid it on a regular basis, so that Botellónes are banned in most cites and federal countries of spain.
Also in Barcelona the consume of alcohol in public (streets, parks, beaches) is prohibited and fined. I heard about fines up to € 3.000,- – although friends who have been caught just had to pay € 30,-. Still an expensive beer!
So, if you carry your can or bottle do it invisble when a policeman comes close!