Certain spells, like Calm Emotions, allow a character to automatically fail their Saving Throw when resisting the effect:
Each humanoid in a 20-foot-radius sphere centered on a point you choose within range must make a Charisma saving throw; a creature can choose to fail this saving throw if it wishes.
—Calm Emotions, Player's Handbook, pg 221
However, a Sorcerer† casting Calm Emotions could choose to make a character automatically succeed at their Saving Throw with the Careful Spell metamagic:
[...] you spend 1 sorcery point and choose a number of those creatures [that are affected by the spell] up to your Charisma modifier (minimum of one creature). A chosen creature automatically succeeds on its saving throw against the spell.
—Careful Spell, Player's Handbook, pg. 102
So if said sorcerer cast this spell on a group of characters, but chose to protect one of the targets (perhaps so that an existing Charm effect is not suppressed) but the target chooses to fail anyways, what happens? Is the target allowed to make this choice at all, or does the metamagic have precedence over the choice granted by the spell?
†It would have to be a Divine Soul Sorcerer, or a Multiclassed Sorcerer, since Calm Emotions is not on the Sorcerer Spell List