Thanks for responses, everyone.
I think it's rabble-rouser in a smaller scale, but rabble-rouser also seems good for what I'm looking for.
But more specifically, it's someone like a child trying to get his parents' or older sibling's attention by misbehaving and irritating them intentionally.
Oh, it's more like 'high maintenance' that I'm looking for. Someone pretending to be .. like still a cute and precious small kid. Thank you.
Yes, on a smaller scale perhaps. Rabble rouser has the right tone but I don't think it works in literal terms. What are the rabble? They are the hoi polloi, the common people, the people on the street, the working class. A rabble rouser is someone who provokes them into rebellion, into riot. I don't think that is what you mean.
Red's right about the meaning and use of 'rabble-rouser' - it's more a political and social-activism term.
'Spoilt brat' might fit and can be effectively used for adults too, although it slightly lacks intentional aspect.
Grown-ups who need attention and make trouble for their own amusement can be called 'stirrers'. Rather like the real life version of on-line 'trolls'.
'Don't take any notice of him he's stirring us up'.
I associate 'high-maintenance' with relationships - a very demanding partner who needs great emotional investment. It might have other nuances elsewhere.
Histrionic personality disorder is characterized by a long-standing pattern of attention seeking behavior and extreme "emotionality."
Someone with histrionic personality disorder wants to be the center of attention in any group of people, and feel uncomfortable when they are not.
Histrionic itself is defined as an adjective as "overly theatrical or melodramatic in character or style."
As a noun, it means "exaggerated dramatic behavior designed to attract attention."