even bad becomes good with a good man

गुणायन्ते दोषाः सुजनवदने दुर्जनमुखे गुणा दोषायन्ते तदिदमपि नो विस्मयपदम्।

महामेघः क्षारं पिबति कुरुते वारि मधुरं फणि क्षीरं वमति गरलं दुःसहतरम्

सुभाषितरत्नाकरे॥

guṇāyante doṣāḥ sujanavadane durjanamukhe guṇā doṣāyante tadidamapi no vismayapadam|

mahāmeghaḥ kṣāraṁ pibati kurute vāri madhuraṁ phaṇi kṣīraṁ vamati garalaṁ duḥsahataram

subhāṣitaratnākare||

A very enlightening quote from Sujana paddathi in Subhashita Ratnakaram

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Meaning 

Bad things, when they pass through the mouth of good people become good. that is, when good even when they talk of bad things would find something good to say about them..

Virtues and great things when they pass through the mouth of evil minded people becom bad , that is when bad people speak about good things, they give out very bad remarks and find defects which are not there..

This is a common phenomenon.. no one need be surprised about it..

The big black rainy cloud is formed by drinking alkaline, non potable water on the surface of the earth , but these clouds in their turn shower sweet water for all on the earth to drink to their hearts content..

However, a poisonous snake thrives by drinking sweet milk, but by nature the snake spews out only dealy venom..

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word analysis 

दोषाः सुजनवदने गुणायन्ते bad things when put into ,passes thorugh the mouth of good people become good

गुणाः दुर्जनवदने दोषायन्ते virtues and great things when passing through the mouth of wily people become bad and distorted.

तदिदमपि विस्मयपदं न Even if that is true, there is nothing to wonder about it..

महामेघः क्षारं वारि पिबति मधुरं वारि कुरुते the big low rain cloud is formed by drinking or absorbing alkaline water from the earth but it gives out very sweet water through rains

फणिः मधुरं क्षीरं पिबति दुःसहतरं गरलं वमति चा the snake drinks sweet mild but spews out deadly poison