チャイナ is shorthand for チャイナドレス 'Chinese dress / qipao.' 理性のタガが外れる 'the hoops on one's reason come off' is a vivid idiom — タガ are the bamboo/metal hoops that hold a barrel together; when they come off, the barrel (= self-control) falls apart. あぶなく 'dangerously / almost' marks the near-miss.