How to make somebody aware of his/ her mistake?
In the Holy Qur'an
O you who believe! let not (one) people laugh at (another) people perchance they may be better than they, nor let women (laugh) at (other) women, perchance they may be better than they; and do not find fault with your own people nor call one another by nicknames; evil is a bad name after faith,
and whoever does not turn, these it is that are the unjust (49:11)
The Importance of Respecting to the elderly in the Traditions (Hadith)
The Prophet said, "Whoever does not have mercy on your young and does not honour our elderly is not one of us"
When the Prophet was aked who were the most beloved of Allah, he replied, "Those who help others the most."
Imam Jafar said, "Hussain (younger) would never walk in front of Hasan (elder) nor would he begin the conversation when they met, out of respect for him."