The problem is that smack talk is subjective. One man's objective statement is another man's horrific insult. As such, you can never enforce such rules without being biased to at least one poster, one way or another.
Trying to moderate such interactions only leads to more clever ways of getting around said rules, which leads to more pent-up frustrations and bigger, more violent and unpredictable outbursts.
The best course of action is to lay down simple rules (e.g. a common one is no ad-hominem attacks) and let the threads run their course.