I'd like a bunch of good ones for Hobgoblins, since nobody really likes them. Hobbo (not hobo) just sounds too lazy and illiterate, whereas caliban goes the opposite direction. If we want to stick with the middle ground--ripping a bit from Shakespeare, without being too literate sounding--then we could use Kalistus-face, since that's the dead of winter, implying that Hobgoblins look harsh (with the added meta-pun of that month ultimately deriving from a Greek word meaning 'pretty'). Mud hutters sounds too much like mud squatters (a derogatory term for the rural farmers outside of Scientius that they have reclaimed for themselves). Green blood is not only woefully inaccurate, but sounds pretty video-gamey. Would loath work (as a sort of noun version of loathe)? How about goat shagger, or get more creative with air thief? Or goob (as a combo slur with Goblins), or cut right to the chase with savage? Maybe trash-monkey? Or use physical references and call them fat-necks, or insult their child rearing traditions with motherless? Would polly be especially stinging to a Hobgoblins ears? Or instead, we could have a range of insults implying that they all have very small penises--especially the women. Continuing with the emasculating theme: miss, missy, duchess, madam, or your ladyship. Maybe we could just borrow one of David Listers favourite phrases and call them smeg heads. But if you really want to cheese one off, call them anything-elf: dirt-elf, dog-elf, twig-elf, bucket-elf, et cetera.
On a related note, I am rather fond of toad-wart as a slur against Goblins, but then again I freely admit to having enjoyed the Gummy Bears cartoon as a kid. I also think I found my new favourite Elf slur: slant-ear. An insult for Dwarves that I can't take credit for is hair-goblin.