People rise or sink to how you talk about them when they’re not in the room.

How you describe somebody behind their back becomes how everyone treats them, and then how they behave. Call somebody unreliable often enough and the group stops relying on them, which leaves them less to be reliable about, and the description closes around them. The same mechanism runs the other way, and nobody notices it working.

Listen to how you talk about the person you find hardest when they are not there. Try describing them the way you would want describing. Then watch whether what you get back from them shifts over a few weeks.