a right one
we've got a right one here
A set phrase used to humorously indicate that one has encountered someone or something they consider stupid or foolish. You think the moon is bigger than the Earth? We've got a right one here!
a right onea silly or foolish person. British informal
1988 Salman Rushdie The Satanic Verses Quite soon they burst out into uproarious guffaws, we've got a right one here and no mistake.