This is one of my favourites from Thirukkural. I had the joy of immersing myself in it while translating it on Facebook (here).
Even after seeing poison being poured, they will consume it
and converse cordially,
they who seek to be captivatingly civilized and compassionate. 
[பெயக்கண்டும் நஞ்சுண் டமைவர் நயத்தக்க
நாகரிகம் வேண்டு பவர்.]
This is a fascinating kural, with Thiruvalluvar at his poetic best. It grows variously in the reader’s imagination and can be interpreted in many ways.
I like to interpret it this way :
The compassionate, even when they know that poison is being served (poured, not just dropped!), they understand why it is being done and go two steps ahead by drinking it and then having a friendly conversation. They understand the intention behind a hurtful deed being done to them – whether the intent is good or bad doesn’t make a difference to the way they act. They are still full of compassion. Tough indeed!
As with most other kurals that appeal to me, I am reminded of this incident in Gandhi’s life:
When Gandhi was thrashed by the angry Pathans in South Africa for agreeing for a compromise with General Smuts on registration of Indians, he lived out this kural. He understood their intentions, he was going ahead to register himself though he anticipated an assault, he bore the assault without defending, he refused to lodge a complaint against them and bore no ill-will towards them.
What did he gain by such an extreme act of non-violence and compassion? Respect of the Whites (who anyway prosecuted his assaulters on other counts) and his fellow Indians in SA. While there is no stated connection, it is no surprise that his staunchest supporter when he came back to India was a Pathan (Pashtun) – Khan Abdul Ghaffar Khan.
We can see such incidents of personal valour (not just political leadership) throughout Gandhi’s life – when the Whites attacked him at Natal, during his many prison stints, in Rajkot when he stood firm when surrounded by a violent mob, and in Noakhali, Calcutta, Bihar and Delhi amidst immense religious violence.