Never argue with a fool

पयःपानं भुजङ्गानाम्
केवलं विषवर्धनम् ।
उपदेशो हि मूर्खाणाम्
प्रकोपाय न शान्तये ॥

- हितोपदेशः

The milk fed to a snake only increases its venom. Similarly, advice given to a fool leads to aggravation and not peace.

Advice is least heeded when most needed.
Every evil has its remedy, except folly.
Talk sense to a fool and he calls you foolish.