Yep, I've been "karma bombed".  But before we start, we need to establish some ground work.  So, keep in mind, my definition of "karma bombing" isn't the literal and mythical meaning of the word (as no one can "force" me to kill them) -- but the implication.  The implication that the other player, who I'll refer to as "intruder", knows -- full well -- that I am occupying the grind spot, knows that I can't even attempt to get rid of them without losing karma, and ignores these facts or uses them to their advantage.  Also note that it is common knowledge in BDO that grind spots have predetermined-by-the-player-base mob-rotations.

Scenario:

I am grinding a rotation, occupying it, and minding my own business.  I have been the only one there for about 30 minutes.  A guildless player enters the rotation I am obviously occupying and starts killing the mobs in it, ruining the flow of mob respawns and my grind session.  This is according to game mechanics, as grind spots are open and are not instanced.  This allows for meaningful player interaction.  Maybe they didn't see me grinding (not sure how they couldn't)?  OK - I approach them.  Speak to them without being rude. 

"Hey, I'm grinding here right now, mind going somewhere else?  Got 30 more minutes on LS" -- I get completely ignored.  The Intruder continues killing the mobs, right in my face.  OK, I'll try again.  Stand right next to them, the chat bubble over my head, stating I am occupying the spot and requesting they leave until I am done.  Again -- completely ignored.  I do not exist, apparently.

What can I do?  Well, my options are: 

1) PK them until they get bored or leave.  This will cause me to go negative karma and the punishments are severe enough to negatively impact my personal gameplay which cause me to prefer not being negative karma.

2)  Attempt to party with them.  Unfortunately, while this may be a good solution, the game's mechanics heavily discourage this in solo grind spots.  The game doesn't allow this without losing out on progress, especially if you're the strongest member in the party.

3) Ignore them and try to outfarm them.  The person who was there first (me, in this scenario) still loses out on something, that being progress (silver, exp).  Also, some classes do not perform as well in PvE than others, so even if you're stronger at PVP, it doesn't necessarily mean you're stronger in PVE.

4) Change channel.  Let the Intruder (griefer) win.

5) Fight griefing with griefing.  Feed them to mobs.  If they lose a crystal, hopefully it discourages them enough to leave me alone.  This option sucks, becuase it makes me a griefer by being a mob-feeder and I do not like griefing others.  I prefer to mind my own business and only PVP when it's mutual.  But when I am being griefed in this way, what other option do I have that doesn't make me lose out on progress or doesn't let the griefer win?

Every single one of those options leaves ME losing something.  And the last option turns me into a griefer.  When I was in the spot first, minding my own business, how is it fair that I have to lose something / let the griefer win / become a griefer myself when I did not initiate conflict or "rudeness"?  I cannot dec, because they're guildless.  I cannot enjoy a peaceful grind rotaton, because someone else is kill-stealing the mobs in the rotation.  This is karma bombing 101, right here, and it has happened to me a few times in my years here.  Good thing it is not common.  But when it happens, it sucks.  I think the current Karma system is "decent", but not ideal........at the end of the day, it turns the game into who can grief harder or longer in some scenarios.  Grief Desert Online, if I were to be extreme about it lol /s.  It's not that bad, though....it's infrequent enough, at least for me since I play late-night / off-peak hours, usually.  But it does suck, when it happens, and I think that people who ignore this issue / downplay it likely are griefers themselves, but that's me being cynical.