Someone that is a complete idiot that is unable to do anything to save themselves, and must rely on a larger more dominant person to help them. Comes from Belarus, a puppet state of Russia, and princess, a pejorative for a weak person.
"You damn Belarusian Princess, why can't you do anything right."
The combination of an imbecile and a twat, basically a very very stupid person.
(after breaking a pane of glass) "You imbecilic twat, you broke the glass!"