"Kiki, go find someplace else to be!"
There is one scene during the Teal Mask that really rubbed me the wrong way, and made me truly dislike Carmine - not as a character, more how she functions as a plot device.
Quick recap of the festival and the morning after (Spoilers, obviously)
The PC and Kieran are at the festival together, then you find the Ogre Oustin' minigame. After a go at that, Carmine pressures Kieran into doing it himself.
While Kieran is gone, the PC and Carmine see Ogerpon, and the legendary drops her mask.
Kieran shows up, PC tries to share this news, but Carmine talks over them.
Kieran leaves believing that the PC and Carmine were talking about him behind his back. (Sidenote, Carmine didn't seem concerned about this misunderstanding; what does that imply about their relationship?)
Carmine makes the PC promise to keep this a secret from Kieran, citing two reasons.
She's worried that he'll feel left out that he didn't get to see it (so she decides to leave him out, brilliant!)
She doesn't want him running up the mountain at night searching for the ogre (more valid, but I think it's telling that it wasn't the first thing that she was worried about; she says it more as an after thought.)
The following morning Carmine shows up at the community centre and takes the PC to her house to talk to her and Kieran's grandpa.
But, oh, Kieran is there! Then she says, "Kiki, go find someplace else to be! PC's got business with me!"
Kieran runs off angry, the grandpa tells Carmine to be nicer to her brother, and Carmine claims that she was being nice since she didn't hit him (I'm paraphrasing, and no, I don't think that Carmine's physically abusive).
Grandpa tells PC and Carmine the truth about Ogerpon and tells them not to tell Kieran the truth, since he plans to do it in his own time.
Carmine's response to being told to keep Kieran in the dark? "OK, Grandpa... Now I REALLY can't tell Kiki we met the ogre..."
And I'm like, what?! If you wanted to tell him, you could've done it at the same time as you told your grandpa!
Remember her two worries? Kieran feeling left out, and him running up the mountain at night. Well, she decided to leave him out some more, and it's morning! Her concern about his safety is no longer relevant, and she's actively excluding him, when her primary concern was him feeling left out!
The way Carmine acts only makes sense as a plot device; she didn't know that her grandpa knew anything special about Ogerpon. They were just gonna show him the mask to get it repaired. What, was her plan to get the mask fixed and return it without Kieran ever knowing? Or to bring him along when they returned the fix mask?
What exactly was this girl's thought process?