Fortiter in re, suaviter in modo

Resolutely in action, gently in manner. Accomplishing a mission, a goal or goals with definitive, decisive manners but doing it tactfully, and by less offensive means.

Жесткий на деле, мягкий в обращении
Так говорят про людей, которые внешне приветливы, а на деле враждебны