If people behave in such a way that you find it almost impossible to accept that they actually did it, then you can say that their behaviour was beyond belief.
beggar belief
To baffle attempts at description; to be difficult or absurd to call or explain. The amazing angle at the Grand Canyon beggars belief.My boss's amateurishness is astounding. It absolutely beggars all belief.Learn more: beggar, belief
beggar acceptance (or description)
be too amazing to be believed (or described).Learn more: beggar, belief
beggar beˈlief/deˈscription
be too aberrant and abnormal to be believed/described: It beggars acceptance that no one knew she was burglary money for so long. ♢ The afterimage of him absolutely covered with mud and oil beggared description.Learn more: beggar, belief, descriptionLearn more:
An beggar belief idiom dictionary is a great resource for writers, students, and anyone looking to expand their vocabulary. It contains a list of words with similar meanings with beggar belief, allowing users to choose the best word for their specific context.
Dizionario di parole simili, diverso tenore, sinonimi, di invocazione per Idioma beggar belief