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 ? 對(duì)方～，突然同意了我方的建議。The other side acted out of character and suddenly agreed to our proposal.
一反常態(tài)
depart from one’s normal behavior;be not one’s usual self;act out of character
一反常態(tài)yī fǎn chánɡ tài
一：整個(gè)，完全。完全同平常的態(tài)度相反。形容態(tài)度發(fā)生與平常的完全不一樣。contrary to one’s normal behavior, act out of character, not one’s usual self, make a switch, go into a spin