"I didn't intend Brainbomb any offence. Brainbomb and I have settled any differences we might previously have had and our recent exchanges have been friendly. If Brainbomb found the OP offensive then I apologise (but I don't get that impression). Whereas, DemonOverlord clearly set out to troll me in a way I find quite upsetting. I don't think it's acceptable to call someone a racist as a "joke"."
And, what, you and DO previously had a history of strife and mutual hatred that justified you in attributing the most uncharitable motives possible to DO's comments? Once the bar has been set at 'jokingly insulting each other', the bar for 'jokingly calling each other racist' is in the same league. The major initial difference is in how you imputed motives, rather than in the actual quality of the joking insults. Of *course* you're just joking around and brainbomb knows that because you're such pals, but DO, no, DO's out to get you! Except, wait, it was a joke like yours...but no, *DO's* joke was unacceptable vicious trolling, because DO's out to get you! You haven't been going after Octavious for the same joke, because after all, *he's* not out to get you, DO is!
And then DO *actually* trolled you for it. Which is the part of DO's behavior *I* think was over the line, insofar as this forum has lines to begin with (cue Al complaining about forum moderation). The "haha can't you take a joke obviously you're *actually* <insult>" shtick is so tired and stupid, and it marks the point where the jokester *cannot* be aiming for mutual amusement and is instead simply infuriating her target by attacking him, whether out of bemusement at his taking offense, or simply for shits and giggles.