Fairness becomes real when it costs your side something too.

Any principle you only apply when it favours you is not a principle. Fairness becomes real at the moment it costs your team, your friend, or you personally something you wanted, because that is the first time it has actually constrained anything. Until then it has been a preference with better vocabulary.

Look for a case where a standard you defend loudly would cost your own side. Apply it there once, visibly. That single act does more for your credibility than any amount of argument.