Just remember to report and ticket but not talk to the person doing it. If you try confronting said person before reporting, it becomes an interpersonal dispute instead of one sided harassment and it's far more unlikely that Blizzard will get involved.
That right there. THAT RIGHT GOD-DAMN THERE. If you are getting harassed, don't try talking to the person to try and settle the matter like adults, just report and walk away, and I am NOT being nasty here.
I can attest, personally, that trying to be an adult with online griefers like the screaming mongoloid our OP has described only nets them a slap on the wrist and an apologetic response from the GMs. The instant somebody starts to get nasty on you, and I mean nasty as in throwing homophobic comments / death threats / slander / religious bile around, hit the report button and hunker down till the GMs can deal with them.
Sadly, the instant you make contact with the offending player personally, it becomes a situation where Blizzard is unwilling to step in. Contact their Guild Leaders and ask them to stop it, if possible, or if not ... report button. Civility and mature discussion nets you nothing within the framework of this game, against the sort of mono-brow twits that think they are 'hilarious', or worse still, perfectly justified to go out of their way to harass and harm other players.
I'm just going to quote this because it needs to be expressed repeatedly until everyone understands it. We've all been raised with the concept that being an adult is learning how to talk through conflicts. It's something you are going to have to break yourself from, because the moment you muddy those waters with trying to 'talk reasonably' with someone, it stops being harassment and starts being a difference of opinion. This is the same irl, on other websites, etc. etc. etc. The MOMENT you respond you have changed it from unwelcome attention, to retaliating with moderator actions because they don't share your opinion. Because obviously if you like them enough to respond to them as a mature adult, you aren't being harassed. The gms are not in the heat of this situation and are keenly aware that you are BOTH human beings who may both have valid sides to the story, so they step back unless it's cut and dried that very clearly this is a case of harassment and not just two friends who are suddenly full of hate.
I know it's a difficult concept to grasp, but it's one that people have been using to get away with harassment scott free for years now, often goading you so that you DO react typically to 'be the better person' and talk things out. Being the better person these days means *walking away*. It means not spreading the rumors around as well. If someone says "Well I heard x and y and z" just laugh and shake your head and say "the rumor mill isn't my thing." If someone wants to believe x and y and z? I hate to say it but.. they're not worth your time. This is game time, not 'justify your reputation' time. Believe me, it's taken me years to learn how to let go and just walk away from things I feel are unjust because it's *MY* reputation on the line.
At the end of the day, you need to decide what is more important to spend your time on. Focusing on these rumors, etc, or finding the fastest way to get it out of your hair so you can continue with the entire reason you've logged onto this game to begin with. Playing. The best thing you can do for yourself is be aware of when you are devoting your attention to things like this person's reputation bashing, and walk away. Be creative, be inventive in the ways you remove yourself from it and go on to have fun. It *can* happen and it is entirely possible to enjoy the game even with someone flailing about and actively trying to ruin your good time.