I am actually rather fond of racism, bigotry and general ignorant types of hate in my writing. Its a wondrous motivator that will make people do brash and strange things, and its a bit silly to ignore that sort of flavor in a fantasy RPG. Here he are some derogatory and colloquial names that would pop up here and again.
Halfling - Peck (my favorite, and the only good thing to come of Willow), Bigge, Hakkaches (Elf term meaning hack cheese), Fillecun or Wydecunthe (very derogatory Dwarf term towards a halfling female, best not described), Yrento (meaning iron-toe or hard-ass)
Elf - Brekelaunce (broken-lance), Mooner (many of their ritual are at night), Winesipper, Pichachas (very derogatory), Aydunken (Dwarf term, meaning acts like a drunk), Strokelady (very derogatory Halfling term, meaning an elf women who will never get any), Smalbyhind (Dwarf term for elf women of small assets)
Dwarf - Cogger, Hooder (many dwarves wear hooded garments), Mudape (very derogatory), Brekaldoun (all breaks down), Fayrandgode (elf term describing a very ugly dwarf), Turnhound (even hounds turn away)
Human - Windsfirst (essentially calling them cowards), Booster, Eyegone (blind to all but what they want to see), Gobyweye (Dwarf term, meaning get out of the way dumbass), Haldebytheheved (Elf term, basically meaning /facepalm)
Nobles - Swetemouth (a liar), Horsmongere (thief by the words of law), Vnderegge (out of his freaking mind), Nobscoiner (Nobles who mark gold coins to give to beggar, coins which are punishable by death to actually spend)
Commoners - Gidye (mad vagrant), Reedcruut (diseased), muck-dweller, inheffelde (one who knows toil), tauth (elf term, meaning without home), Orechinnio (dwarf term, meaning one who trades anything for ore)
Use some of these terms would be grounds for a duel to the death. Others are fairly light hearted.
I think I had far too much fun writing that..