Summary: Bringing up information unrelated to the negotiation issues.
Some counterparts specialize in inserting a tangent, or side issue, into a negotiation that has absolutely nothing to do with the negotiation being discussed.
Example
A manager is discussing with an employee the importance of coming to work on time. In the middle of the discussion, the employee protests, “Other employees come into work late, and you do not say anything to them.” This is an example of Launching a Tangent to deflect attention from the real issue: this employee’s continual tardiness.