Continuing to laugh and joke with your fellow Muslim, without advising him if he does something wrong is betrayal.
Backbiting and Brotherhood
It is reported that Al-Fudayl b. ʿAyyāḍ said, “When backbiting appears, brotherhood for Allāh will disappear; and at that time you will be like things plated with gold and silver: wooden on the inside, [merely] looking good on the outside.”
Abū Nu’aym, Hilyah Al-Awliyā`, Vol. 3 p395.
Also read
Related sayings.
Some of the evils that come with loving authority and seeking power.
Birds of a feather flock together. The souls of men are allied, like with like.