Those who have a habit of swearing frequently should not assume that they will not be punished for this. (It is not possible to mention every single swear word that people say these days but here are two examples). Calling someone a ‘Walad-uz-Zinā’ or ‘bastard’ or calling a chaste woman an ‘adulteress’ (this is common amongst women these days when they lose their tempers) are all examples of slandering and are Ḥarām and grave sins. Here it is not a valid excuse to say, ‘I just said it without thinking, I didn’t mean it’.
Remember! There is punishment in the afterlife for this, but even in this earthly life in some cases there are severe penalties. For example if a man or woman calls another chaste man or woman an adulterer or adulteress and the case is presented to an Islamic ‘Adālat [i.e. court] and the accuser cannot present four eye-witnesses then the accuser will be given 80 lashes and will never ever be a reliable witness in any matter. (These rules apply if the accused is a man or woman, Muslim, free, sane, has reached puberty, and is chaste.)
Accusing someone of adultery is called ‘Qażaf’, the accuser is a ‘Qāżif’ and the penalty issued by an Islamic court is called ‘Ḥadd-e-Qażaf’. Anyhow there are only two things that can save an accuser (male or female) from this penalty: (1) If the accused admits his or her crime or (2) the accuser presents such four witnesses in front of the Islamic ruler who saw, with their own eyes, the man and woman fornicating. It is not easy to see this and even more difficult to prove it. So the safer way out is that even if a person does become aware of someone committing fornication they should not tell anyone. This way, the filth remains where it is, because if anyone mentions it and cannot provide four eye-witnesses then the accuser should be prepared to suffer 80 lashes if the accused files a case against him.