It is unlawful for a Muslim to desert his brother Muslim

Narrated Abu Aiyub Al-Ansari:

Allah's Apostle (may peace be upon him) said, "It is not lawful for a man to desert his brother Muslim for more than three nights. (It is unlawful for them that) when they meet, one of them turns his face away from the other, and the other turns his face from the former, and the better of the two will be the one who greets the other first."

[ Sahih Al Bukhari : book 73, hadith 100 ]

Narrated Anas bin Malik:

Allah's Apostle (may peace be upon him) said, "Do not hate one another, nor be jealous of one another; and do not desert one another, but O Allah's worshipers! Be Brothers! And it is unlawful for a Muslim to desert his brother Muslim (and not to talk to him) for more than three nights."

[ Sahih Al Bukhari : book 73, hadith 99 ]

I think a lot of people are guilty of not following this hadith ( including myself ) , it's always easy to be angry and sever ties with our family and friends, but the first one to make amends is definitely the better Muslim.
I think we should at least put in some effort to be cordial and greet each other respectfully, our social behavior is what differentiates humans from animals.

Abu Huraira, r.a., said, "I heard Abu al Qasim (the Prophet saaws), say, 'The best among you in Islam are those with the best manners, so long as they develop a sense of understanding.' "

[Hadith - Bukhari's Book of Manners #286 ]