straighten up
phrasal verb with straighten verb uk/ˈstreɪ.tən/ us/ˈstreɪ.ən/
(POSITION)
挺直身体，直起身
to stand straight after bending at the waist
(BEHAVIOUR)
US改邪归正，改过自新
to behave well after behaving badly
You'd better straighten up or else! 你最好改邪归正，否则有你好看的！