Simple. If the prick isn't smart enough to like his sovereign (bad relation, f.i. -50), he's a traitor, by definiton.
If a vassal strongly dislikes you, he will break his oath, sooner or later. As the in-game description says, it's only a matter, then, of who strikes first. If you let him choose the moment, it will probably be when you can least afford it. If you indict him, you will piss off the other vassals, but at least you won't lose any land.
It's a losing position anyway, and best avoided in the first place. A relation of something like -50 may be mendable, but it'd be quite a tremendous task.