Hmmm. Believe it or not, I used to get this a lot. I as expected to the mediator/peacemaker but I was expected to do it in whatever way "they" wanted so I killed two birds with one stone:

Two Birds:
1. Mediate for us but do it the way we want you to instead of the way you would be more comfortable doing it, if, indeed, you are comfortable at all. (Which we think you might not be but we don't care because we are hopelessly self-absorbed.)
2. Mediate for us even though we don't actually want to solve the problem at hand or listen or make progress or compromise on anything like that at all ever.

One Stone:
Be as direct and uncompromising as possible in my mediation. They hate it when you say things like, "So, we are at a standoff because you want your way in every situation no matter how trivial and petty, and you, over there, are refusing to give even an inch on something this trivial because you want nothing more in life than to make sure s/he doesn't get anything their way at all ever. The rest of us have to endure your endless bickering and stupid games and process strife and grief that we are neither interested in nor pleased, in any way, to be forced to deal with. Thus, you're both being childish assholes and I will treat you accordingly. Shall we begin?

That tends to stop people from asking you to help. It certainly worked for me.

I don't like being rude (no, really) and I genuinely like to help people when I can but there is a limit to my goodwill and how much of my time and energy I should be expected to waste on situations like this. If you are going to be upset about something like this (and it always upset me the way it upsets you), might as well get something out of it.

It actually doesn't surprise me that you've been put in this position also.

Thanks for the thoughtful reply... food for thought.

An invitation now stands to come drink with me/us.

The key question you asked was "Why do people waste my time with catty complaints about other people?" and that's the part I'll answer.

They just want someone else to solve their problem for them because a) it's easier than doing it themselves, and b) they have someone else to blame if it fails.

In a world where personal responsibility is rapidly becoming as rare as common sense, it comes as no surprise.

Wil: I'd like a nice red beer, please.

Blogless Mike: (can I abbreviate that to BM? Heh.) You're right. I actually did say a few choice words about personal responsibility that day.