Yankees and Red Sox. Red states and blue states. Your seven-year-old and your nine-year-old. Humans, it seems, are wired for disagreements. These conflicts can be angry, awkward messes, or they can be civil exchanges of viewpoints that lead to better decisions at work and closer relationships at home. What makes the difference is usually not the issue at hand but how it is handled. Here, then, are the rules of engagement, followed by tips on how to speak your mind (to almost anyone). No bench-clearing brawls, no threats of secession, no backseat turf wars involved.