In CK2 you can transfer your vassals under other vassals. Vassals do not get a say on this, it happens immediately.
From gameplay the perspective, it allows you to sweep disloyal vassals under the carpet, and it's gamy for that reason.
From a historical perspective, it's worse. The direct vassals of a sovereign are known as "tenant-in-chiefs", their stature is known as immediacy. Every vassal wants to have immediacy, for it assures a bunch of privileges and demands attention from the overlord. What happens when everybody gets immediacy is that of the 15th century Holy Roman Empire; so for the sovereign, it isn't ideal to hand them out like candy.
But the point is that immediacy is a valuable thing to have, something nobody wants to give up, but that is exactly what interaction "transfer vassalage" does. By placing them under a former peer, they lose their immediacy and become a mesne lord. While immediate count and a mesne count have the same title, they are not equal.
The act of removing one's immediacy is known as mediatisation, and it shouldn't be done lightly. As stated before, the lords really value their immediacy, and I would go as far as to say that no lord would willingly be mediatized. Thus I reckon, the only way to mediatize irritating a vassal should be when you have them imprisoned. Naturally, transferring non-feudal vassals such as viceroys and mayors do not count as mediatisation and should be done at will.
Now, I know restricting mediatisation would make the game more difficult, but truth to be told, this is something that many rulers struggled with. If you can't keep your vassals from obtaining illegal immediacies and can't enforce the policy of mediatisation, you deserve to be over the vassal limit and find yourself in the same jam as the 15th century Holy Roman Empire or any other decentralized state.
From gameplay the perspective, it allows you to sweep disloyal vassals under the carpet, and it's gamy for that reason.
From a historical perspective, it's worse. The direct vassals of a sovereign are known as "tenant-in-chiefs", their stature is known as immediacy. Every vassal wants to have immediacy, for it assures a bunch of privileges and demands attention from the overlord. What happens when everybody gets immediacy is that of the 15th century Holy Roman Empire; so for the sovereign, it isn't ideal to hand them out like candy.
But the point is that immediacy is a valuable thing to have, something nobody wants to give up, but that is exactly what interaction "transfer vassalage" does. By placing them under a former peer, they lose their immediacy and become a mesne lord. While immediate count and a mesne count have the same title, they are not equal.
The act of removing one's immediacy is known as mediatisation, and it shouldn't be done lightly. As stated before, the lords really value their immediacy, and I would go as far as to say that no lord would willingly be mediatized. Thus I reckon, the only way to mediatize irritating a vassal should be when you have them imprisoned. Naturally, transferring non-feudal vassals such as viceroys and mayors do not count as mediatisation and should be done at will.
Now, I know restricting mediatisation would make the game more difficult, but truth to be told, this is something that many rulers struggled with. If you can't keep your vassals from obtaining illegal immediacies and can't enforce the policy of mediatisation, you deserve to be over the vassal limit and find yourself in the same jam as the 15th century Holy Roman Empire or any other decentralized state.