The instinctive emotion of evil is selfishness. That means the evil person has no sympathy for anyone else, even another evil person. He does not show tolerance to anyone; he is even repelled by the evil characteristics of his fellow.
י = נֶפֶשׁ רָשָׁע אִוְּתָה רָע לֹא יֻחַן בְּעֵינָיו רֵעֵהוּ
(10) The soul of the wicked person craves evil,
but his evil friend will not find favor in his eyes
Even though a wicked person sees the ugliness in the evil behavior of another wicked person, he can easily excuse his own evil behavior. He tolerates his own behavior because it gives him pleasure, but he is intolerant of such behavior in others.
(10) The soul of the wicked person — נֶפֶשׁ רָשָׁע
craves evil, — אִוְּתָה רָע
because it gives him pleasure
but he finds nothing to like — לֹא יֻחַן בְּעֵינָיו
in his fellow. — רֵעֵהוּ.
 The wicked person does not really believe that what he is doing is proper and that is why he is intolerant of such behavior in others. (רלב”ג).
 A fellowship of wicked people will end up quarreling because each one finds the ugly habits of the others hateful. (מלבי”ם)
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Mishlei 21-10 (Selfishness) PDF version