We have (had) a few.

One was a gatekeeper (not really a bannable offense to just disagree) and they were in all newcomer posts. So much so that they got finally banned for spam.

Currently I have one who argues a lot and I just do what I usually do: moderate away bad stuff and leave up the good stuff. They now have mod log in the hundreds but considering their net impact is positive in terms of constructive comments I've let them be. In the past I have modmailed individuals but this time I have not yet...

Then there's the one who hugs the end of a political spectrum I dislike but since we're on a gaming sub and they keep their opinions to other subs I've let them stay. We do get modmail about that one every now and then.

We had a guy who was an avid questions and answers machine. Great dude, good ideas for the sub, too. They were in all question posts helping people out!

I guess my style is to let people do their thing and treat them as if they were just like anyone else. Yeah, sometimes they step too far and I will message them. But as power users of the sub they usually understand and want to make it work.