The responsibilities of a Muslim towards family, relatives and other Muslims in general, were already reviewed in an article. Here one's responsibility in Islam towards neighbors, friends, and enemies are discussed.

The Responsibility in Islam Towards Neighbors 

Doing good to neighbors is highly emphasized in Islamic teachings: “Worship Allah and … be good to … the near neighbor and the distant neighbor” (4:36). Prophet Muhammad (PBUH&HP) advised Imam Ali (AS) to honor the neighbors, even if they are disbelievers (Kafir) [1]. Imam Ali (AS) said that Prophet Muhammad (PBUH) used to invite repeatedly to doing good to neighbors such that we thought he (PBUH) was going to consider an inheritance for them [2].

The rights of neighbors on one another as an important responsibility in Islam, are:

To honor them in their presence, and to help and care about them when they are absent [3]. It includes visiting neighbors when they are sick, to assist their funeral, and to offer them your tasty meals that smell good [4];
To keep their secrets. It means that not to look for their faults and errors. And, if ever you become aware of some of their faults, do not reveal them but try to conceal their deficiencies [3];
Do not leave neighbors alone in difficulties [3]; e.g., help them in case of financial needs [4];
Do not be jealous of them if God grants them some blessings [3];
Ignore their errors to yourself and forget about them. If ever they do wrong to you unintentionally, be patient and in peace with them [3];
Do not let others talk behind their back and reveal the deficiencies of your neighbors here and there [3].
Giving priority to the neighbors. It is narrated from Imam Hassan (AS) that Lady Fatima al-Zahra (AS) used to pray firstly for the neighbors and then for members of the family [5]. 

According to Imam Sadiq (AS), having good behavior and interaction with neighbors increases the provision (Rizq) [6]. Prophet Muhammad (PBUH) advised to respect neighbors as much as one should respect his\her mother [6] and he (PBUH) said: “God bless whoever does good to his\her neighbors” [7]. On the contrary, whoever sleeps peacefully at night while one of the his\her neighbors is hungry, God will deprive him of his blessings on the judgment day [8]. The same will happen to whoever annoys his\her neighbors [1]. 

Take your time and think about these attitudes towards the neighbors. Life will be surely much agreeable and peaceful if we improve our social interactions with our neighbors within the Islamic framework.

The Rights of Friends and Companions

Having a good companion is known as a blessing; on the contrary, a bad one is like a disaster [9]. Friends and companions have certain rights one over the other including:

To interact with them with generosity as much as you can, otherwise, be fair to them [3];
To be smiling when you meet them and to receive them modestly [3];
To respect them as they respect you [3];
To be the first one who does good to the other one, otherwise, try to compensate properly [3];
To help them in difficulties and whenever they are in need, as Imam Ali (AS) advised to [10];
To hold them in great affection according to Imam Ali (AS) [11];
Not to reveal their deficiencies and mistakes;
To encourage them in obedience to God and to prevent them from committing sins [3];
To be honest with them and not to cheat [3]; e.g., nor to talk behind their back neither to reveal their deficiencies and to guard their secrets;
To be trustworthy whenever they rely on you [3].

The Responsibility in Islam Towards the Enemies

The enemy here means a person whom one is in conflict with. There are some recommendations in Islamic resources on how to treat enemies and what is one's responsibility in Islam towards them:

To be fair with them [12]. According to Imam Sadiq (AS), a real believer (Mu'min) does not oppress his\her enemies [13];
To testify in favor of the enemies if they are right [14] even if your testimony is against yourself [3];
To keep the promises you made to your enemies [15];
To forgive and tolerate them, if possible [3]. According to Imam Ali (AS), there is a virtue in forgiving enemies [16];
To talk nicely and shortly with whoever you have complained of [3], to argue with them in a way that is best (16:125), and not to ignore their rights if ever you are wrong [3].

References:

1. M. Shoueiri “Jami’ al-Akhbar”, p. 84.
2. Shaykh al-Kulayni, “Al-Kafi”, vol. 7, p. 51.
3. Imam Zayn al-'Abidin (AS), “Treatise On Rights (Risalat al-Huquq)”.
4. responsibility towards others
5. Shaykh al-Saduq, "Ilal Al-Shara'i", p. 181
6. Shaykh al-Kulayni, “Al-Kafi”, vol. 2, p. 666.
7. Shaykh al-Saduq, “Al-Amali”, p. 288.
8. Shaykh al-Kulayni, “Al-Kafi”, vol. 2, p. 668.
9. “Ghurar al-Hikam wa Durar al-Kalim”, T. 4719-4720.
10. “Nahj al Balaqa”, p. 494.
11. “Ghurar al-Hikam wa Durar al-Kalim”, T. 9665.
12. Ibn Shu’bah, “Tuhaf al-Uqul”, p. 88.
13. Shaykh al-Kulayni, “Al-Kafi”, vol. 1, p. 47.
14. Shaykh al-Saduq, “Sifat al-Shia”, p. 24.
15. “Nahj al Balaqa”, p. 53.
16. “Ghurar al-Hikam wa Durar al-Kalim”, p. 435.

A feature that is being propagated by different types of media about Muslims and Islam is an angry and aggressive face. This is while Islam has a lot of direct commands and recommendations about controlling anger and being good-tempered. A narration from Imam Sadiq (AS) defines good-temper very well: “Good temper is to soften your attitude and clear your speech and meet your brother with kindness.” [1]

In this text, we will study the viewpoint of Islam on being good-tempered.

Direct recommendations from the Quran

There are many verses of the Quran that teaches us how to interact with others. The Prophet of Islam (PBUH&HP) was sent as a role model: 
“There is certainly a good exemplar for you in the Apostle of Allah—for those who look forward to Allah and the Last Day and remember Allah much.” (33:21) 

This exemplar is defined in different verses of the Quran, not only by admiring the number of his prayers but with his excellent manners. Allah admires his apostle by saying: 

“And indeed, you possess a great character.” (68: 4)

Therefore, when Allah tells us: 

“Obey Allah and the Apostle so that you may be granted [His] mercy” (3: 132), He means that by following the characteristics of the Prophet (PBUH&HP), one can achieve success and prosperity. One of his most important features was his good-temper. 

The effects of being good tempered on achieving success

One may think that many people are not good-tempered and yet have very successful lives. However, the Quran introduces being soft and kind to people as a means of reaching goals. 
Almighty Allah says to His Apostle: 

“It is by Allah’s mercy that you are gentle to them; had you been harsh and hardhearted, they would have surely scattered from around you. So excuse them and plead for forgiveness for them, and consult them in the affairs, and once you are resolved, put your trust in Allah. Indeed Allah loves those who trust in Him.” (3: 159)

As it is mentioned in the above verse, Allah introduces being good-mannered and good-tempered as the essential element that made the Prophet (PBUH&HP) successful in guiding people. Also, some of the features of a good-tempered person are mentioned in this verse:

1.To be forgiving towards people’s faults and mistakes in our social or family life (Excuse them). 

2.To ask Allah to forgive other people for their sins and mistakes (plead for forgiveness for them). Having this manner helps us feel real compassion towards others, and therefore, it allows us to interact with them with kindness and a good temper. 

3. To give credit and respect to other people by asking their ideas even if we know better than they do (consult them in the affairs). 
Imagine that if in our daily life, we try to consider these three crucial hints, how peaceful our life will become, and how influential we can become in our relations and communications.

To Whom should we be good tempered?

Should we be soft and gentle to everyone? Or are there groups of people to whom we should be harsh and demanding? 

Two verses in the Quran explain how Muslims should behave towards different groups of people. This verse of the Quran: “Muhammad, the Apostle of Allah, and those who are with him are hard against the faithless and merciful amongst themselves,” (48: 29) indicates that Muslims should be kind and merciful to other Muslims and harsh on those who deny the existence of Allah and the hereafter. However, when Allah orders prophet Moses (PBUH) and Aaron to go to Pharaoh to invite him to monotheism, He orders them: 

“Both of you go to Pharaoh, for he has indeed rebelled. Speak to him in a gentle manner; maybe he will take admonition or fear.” (20: 43-44)

 Again, in this verse, Allah introduces the importance of soft and gentle speech as an essential means of reaching goals.

 The effects of being good tempered in our life

Experience shows that by being good-tempered, one can become popular among others and can make his/her own life as well as others peaceful. 
Prophet Muhammad (PBUH&HP) says: 

"being good-tempered sustains friendship.” [2]

Imam Al-Sadiq (AS) says: 

“Charity and being good-tempered flourish lands and increase lifetime.” [3]

And in the words of Imam Ali (AS): 

“The treasures of the provision are in being good-tempered and affability.” [4]

These verses of the Quran clearly show that if people wish to have a good life in this world and the hereafter, they need to work on themselves to control their anger and to be good-tempered in their relationships.  

References:

1. Bihar al-Anwar, vol. 68, p. 389
2. Bihar al-Anwar, vol. 71, p. 389
3. Bihar al-Anwar, vol. 71, p. 395
4. Bihar al-Anwar, vol. 75, p. 53