I am currently an op on a channel (not registered.. yet

)
We've had some.. unwanted people which resolved into a permanent ban.
However..
This person who was banned from our channel has been running the mKill like a nutcase. He has an undernet-host.
Last night he nagged to me on MSN on how "low security" we had on our channel. And how he felt "obligated" to share his consurn.
Basicly, I told him to stuff it....
Earlier this night, he joined the channel, did a takeover on an undernet-registered user to give himself op. Just to "prove his point".
One of our opmembers spotted this before he could do any form of "damage" and got him out of the channel again.
Obviously, talking to this person hasn't helped.
Sending pm/notice hasn't resolved in any response.
We've tried joining the same channels that he has been on, in order to at least get _some_ kind of response. But considering that he has axx on most of the channels he's on, we've been kickbanned from them.
(And yes, I was polite)
Once he even told me to "wait a sec" just so he could op himself and kick me out. Needless to say.. I'm hello.
What do I do? And how do I do it?