It is simple, report them. the option is there. Blizz keeps tracks of reports on players and when they add up the bans start, progressing until it is permanent. The thing is YOU have to report them, not just come here screaming 'mummy Blizzard mummy Blizzard there is a nasty person make him stop'.
YOU can add them to your ignore list, no matter what server they are on, and you will never group with them again so they will never bother you again.
If someone has 1 bad day and behaves badly once, nothing will be done.
If it is an ongoing problem and multiple people report it, action will be taken, but people have to report it. If they do not, Blizzard will not, usually, ban someone for 1 episode although there are exceptions.
Also, Blizzard has to agree that what they say is toxic. I, on occasion, call whining brats in game 'bed wetters' before I put them on ignore which means I do it once. Blizzard has never found that toxic enough to ban me though I have been, according to the nappy brats, reported, sometimes by a group of friends trying very hard to get me banned. They may object to me calling a 16 year old a bed wetter but Blizzard does not, but I think he probably thinks it so toxic because he is one. Toxic may just be your point of view.