Imam Ahmed Alhasan (a.s) says in the book The Enlightening Answer across the Ether volume:
As for cursing and insulting, this is not from our manners. And I ask Allah that He bestows upon me and make me among those who forgive the ones who have offended them. And I seek refuge in Allah from being tough and vicious. And I have forbidden the believing brothers and the believing sisters from [having] bad manners which would offend them firstly and would offend the Islam which Muhammad has come with secondly, considering [the fact] that they are affiliated with him (peace be upon him and his Family). And I have asked them to possess the morals/manners of the Qur’an. And many of them know how many times I have asked them to read some chapters that show the Divine Morals/Manners and work by them. So mocking, cursing, insulting, name calling, offending the honor of people, and every manner by which Allah is not pleased, is unacceptable and is absolutely completely rejected according to us, we do not accept it, and we do not accept that any believing brother or sister posses it.
And peace, mercy, and blessings of Allah be upon you.
Ahmed Alhasan
Dhul Q’ida 1430 Hijri
The Arabic version:
أما بالنسبة للسب والشتم فليست من أخلاقنا وأسأل الله أن يمن عليّ ويجعلني ممن يغفرون لمن يسيء لهم، وأعوذ بالله أن يجعلني جباراً شقياً، وقد نهيت المؤمنين والمؤمنات عن الخلق السيئ الذي يسيء لهم أولاً وللإسلام الذي جاء به محمد (ص) ثانياً باعتبارهم محسوبين عليه ، وطلبت منهم أن يتحلوا بأخلاق القرآن، ويعلم كثير منهم كم مرة طلبت منهم قراءة بعض السور التي تبين الأخلاق الإلهية والعمل بها، فالاستهزاء والسب والشتم والتنابز بالألقاب والتعرض لأعراض الناس وكل خلق لا يرضاه الله فهو منبوذ مرفوض رفضاً قاطعاً عندنا لا نقبله ولا نقبل أن يتخلق به أحد من المؤمنين والمؤمنات
First Mahdi : Yamani : Ahmed Alhasan 