An extremist, to me, is more easily defined by one’s behaviour rather than
labelling the person and then it seems a lot easier to define:

ie Behaviour where anyone that is extremely disagreeing or anyone that is extremely agreeing.

Extreme Agreeing: as in not speaking up when one is in disagreement or over emphasising their agreement by using such clichés as “absolutely, exactly, perfect or you’re so right, etc”

Extreme Disagreeing: as in becoming angry in one’s decent, and using words like “impossible, that’s bullshit, you can’t always…, why do you never, etc”

Both, to me, are extreme behaviours or the beginning of extreme behaviour and if left unchecked, I think will result in problems within relationships in organisations and teams.

The irony is that one extreme behaviour is likely to elicit and attract the opposite extreme behaviour from the other, creating an environment that initially seems stable but will eventually self destruct given enough time and participation.