Answer:

a)    God, the holy prophet (P.H) and the holy imams have prevented Muslim to use bad words even for He enemies. As the holy Quran introduces the holy prophet’s (P.H) leniency as a factor for him to be attracted.

فَبِما رَحْمَهٍ مِنْ اللهِ لِنْتَ لَهُمْ وَ لَوکُنْتَ فَظاً غَلیظَ القَلْبِ لا نْفَضُوا مِنْ حولِک (آل عمران/159)   

     It was by the mercy of Allah that thou wast lenient with them (o Muhammad), for if thou hadst been stern and fierce of heart they would have dispersed from round about thee.

     Also, the holy prophet stated:

اِنً اللهَ حَرًمَ الجَنًهَ عَلی کُلِ فَحاشٍ بَذیءٍ قَلیلِ الحَیاءِ لا یُبالیِ ما قالَ وَ لَا مَا قیلَ لَهُ[1]

     Surely, Allah has made it illegitimate for everyone who uses bad language and is impudent

b)    Using bad language and cursing means asking for punishment for those who are the enemies of Allah and the religion:

ان الذینَ یَکْتُمُونَ ما انزلَنا مِنَ البَیًناتِ وَ الهُدی مِنْ بعدِ ما بَیًناهُ لِلناسِ فِی الکِتابِ اولئکَ یَلْعَنُهُمُ اللاعِنُونَ (بقره/159)

      Those who hide the proofs and the guidance which we revealed, after we had made it clear in the scripture: such are accused of Allah and accused of those who have the power to curse.