act out of character;contrary to one’s usual practice; depart from one’s normal behaviour; make a switch (/an about-face);not to be one’s usual self ❍ 对方～，突然同意了我方的建议。The other side acted out of character and suddenly agreed to our proposal.
一反常态
depart from one’s normal behavior;be not one’s usual self;act out of character
一反常态yī fǎn chánɡ tài
一：整个，完全。完全同平常的态度相反。形容态度发生与平常的完全不一样。contrary to one’s normal behavior, act out of character, not one’s usual self, make a switch, go into a spin