Pre-emptive shunning? As in people avoiding you even before an "official" pronouncement has been made on you (disfellowshipped, dissassociated, reproof)?
There is, or at least was an official JW policy called "marking". In which, or so the talk explained, if you see somebody. Hmm, how can I explain this? If you see somebody who's not exactly breaking rules that get you disfellowshipped, but isn't exactly living up to the high standards the Watchtower lays out for you, you can, if you want, "mark" them. You avoid them and more or less treat them like they're disfellowshipped so as to avoid being corrupted by them.
In the talk about my brother and myself, they mentioned lifting weights, worldly dress or hair styles, going to see rock music concerts, watching R-rated movies, and others. I don't think they were all about us (so far as they knew anyway...), but maybe some general pet peeves that some were doing and others were against.
I transcribed that talk from a recording. If I still have the recording, I might be able to turn it into an MP3 and post a link to it sometime or else I'll post the talk in text form.
Anyway, this "pre-emptive shunning" term is new to me. If you made it up, it sounds like marking and you may want to reword the question to something that's JW-speak so that more will understand the meaning. IF marking is still done.