Nothing gets a person riled up like a good old fashioned trash talk. Altercations usually happen when one person talks trash. Trash talk shows a blatant disrespect for the other party, and nobody likes to be disrespected. When egos clash, anything could happen.
There are some individuals who get a kick out of starting altercations by random trash talk to strangers. They will usually only do this when they are in groups, so they can feel empowered about bullying others. Some people will not take this, so they will trash talk back. Regardless, there is nothing more satisfying than a cocky trash talker getting their just desserts.