On one hand, most of us are adults, and this is a mature MUD. On the other hand, there's a language policy. Also, the phrase "Fuck you" (and similar) is so blunt and powerful that when someone uses it in game, it reaches beyond the game and comes off as a personal insult to the player its directed towards. To me that's inappropriate. I mean sure, maybe we should just have thicker skins, but honestly, you couldn't think of anything else to say? I mean I know Fire Giants aren't smart, but supposedly you are.

Some alternatives I can think of off the top of my head.
"Bogkch." <<just a noise, could be used as a substitute to swearing, like Klingons using "P'tach!" Make up some other foul-sounding words.
"Speak to Kragck again, and Kragck will crack your skull tween his toes."
"Piss on yer head, yar."
"Get squished, little man."

Or maybe just don't reply at all. Because a character of mine would've just growled or snarled and spat and not responded. Guy's not worth the chatter. He's especially not worth making yourself look dumb.

Then again, I have no idea how annoying or obnoxious morocco may have been, maybe the player did deserve a personal fuck off. But I still don't think it warrants it. Just take the higher road. But that's just my opinion.