To get this achievement, it's best to play with two (or more) controllers. have yourself on one side, your 2nd controller on the other side. You don't even need to sign in an account on the second controller.
Keep the second controller near his goal. With your main account, just walk the puck into the goal, then quickly turn to face your opponent, and press A to shoot the flaming puck at your opponent. If it kills them, this is a disrespect. A slam dunk is when you walk the puck into the goal.
You can see this method in my video below: