The following is not something we either experienced or even considered on our visit to Potosi, but the description from Lonely Planet seemed so bizarre that I thought I would include a quote:
Tinku – The Art of Ritual Mayhem
Native to the northern part of Potosí department, tinku fighting ranks as one of the few Bolivian traditions that has yet to be commercialized. This bizarre practice lies deeply rooted in indigenous tradition and is thus often misunderstood by outsiders, who can make little sense of the violent and often grisly spectacle.
Tinku may be best interpreted as a means for campesinos to forget the hardships of daily life. Festivities begin with singing and dancing but participants eventually drink themselves into a stupor. As a result, celebrations may well erupt into drunken mayhem and sometimes violence.
This excessive imbibing inevitably results in social disorder, and by the second day the drunk participants tend to grow increasingly aggressive. As they roam the streets, they encounter people from other communities with whom they may have some quarrel, either real or imagined. Common complaints include anything from land disputes to extramarital affairs tot he theft of farm animals and may well result in a challenge to a fight.
The situation rapidly progresses past yelling and cursing to pushing and shoving, before it turns into a rather mystical – almost choreographed – warfare. Seemingly rhythmically, men strike each other’s heads and upper bodies with extended arms… To augment the hand-to-hand combat, the fighters may also throw rocks at their opponents, occasionally causing serious injury or death. Any fatalities, however, are resignedly considered blood offering to Pachamama in lieu of a llama sacrifice for the same purpose.
As you would imagine, few foreigners aspire to witness this private and often violent tradition and many people who have attended insist that they'd never do it again.
I was wondering whether this really exists of whether the Lonely Planet writers just had too much puro on their trip to Potosi. It appears that there are a number of articles on the Internet discussing tinku, including a Wikipedia article. The Wikipedia article, however, is drier than the Lonely Planet description above, and as a result doesn’t communicate the same sense of bizarreness.