Trust me on this, don't do PK clans.
Seriously though, let me tell you my experience on that:
A couple of my friends (good friends) and I went up to the Rogue's Castle to hopefully trap one of my friend's arch enemies there. (This was before the wildy update) One person in our group had his clan coming to help us.
Well, we waited for a good hour for this one clan to show up. And once they did, they slaughtered us. We returned, and after they were told that we were allies, they started a playful attack, where they only attack you once, just to get exp, but not kill. Didn't work out. They killed us each a total of 3 times, knowing full well that we were allies. In the mean time, they were attacking each other playfully, taking each other to dangerously low hp levels.
It may not sound that bad, but when you're in lvl 50+ wildy, you can't take any chances. I wished that the Chaos Elemental would come in and destroy them all
. Sadly, I never saw that part.