Lath

You can try, within your interpretation of their rules. And if you get banned for that, take pictures.

If you have evidence of abuse and selective enforcement of the rules, show it in order to allow the admins to act on it.
Don't just lash out, document the exchange. Keep a record of the favouritism.

Understandable, however, generalities sometimes aren't enough in a court of law.
The difference between the spirit and letter of the law allows for interpretations that don't agree with each other. As we can see in this situation.

And like it or not, this is a social court of law. Moderators and admins are judges who follow the rules and administer relative justice. You can either agree to give them the latitude to have their own interpretation of the rules as long as they stick to them, or you make concise rules that offer no room for discussion.

You might say each instance can have its own rules and that is true, but when those written rules are the same and defederation starts to happen because there is disagreement on the meaning of those words, the "in general" part is going to be the mainstay of how rules are enforced.

And, in general, that's part of what causes societies to fall.

bigotry
ˈbɪɡətri
noun
obstinate or unreasonable attachment to a belief, opinion, or faction, in particular prejudice against a person or people on the basis of their membership of a particular group.

If the person in question went after them simply because they are part of the group called 'tankies', the first rule was broken.
If the person in question was the first to throw out insults, the second rule was broken.

If however the opposing group initiated the conflict, broke the same rules and was not punished, then the complaint here is fair and should be pursued in order to prevent an escalation of abuse.

...

The nasty thing about bigotry is that by definition, it doesn't matter which group is being discriminated against. It accepts all discrimination under its label.