Half of the fun of being a poker player is the social aspect of it. You may not become best friends with the people at your table (you may not even end up liking each other very much), but one thing that poker players can usually count on is a mutual respect from the people who are seated with him. This respect comes from being around folks have the same goal as you, even if it is at odds with your own personal goal. That said it is an unspoken taboo to break that respect at a poker table.
When you see a poker player verbally abuse another player at the table, the disgust of everyone present is palpable. Every person who breaks this rule is immediately shouted down or otherwise ostracized, and it becomes clear that this player has lost his self-control and is playing on tilt, thus making them an easy mark. A player without self-control makes it apparent that he is not at the top of his game. His frustration will make him more prone to play weaker hands and make bad calls out of his frustration.
Take a cue from this tell-when you see someone berate another player, do everyone else a favor and knock him out as soon as possible.