A Yoko Ono
The annoying person who splits up your group of friends, usually by being super popular and stealing your best friend.
My friend got split up with his group because of his new girlfriend, who was a Yoko Ono.
My class got split up because the new kid was a Yoko Ono and stole my best friend.
My brother got split up with his friends because his new friend was a Yoko Ono.