Back for its 15th anniversary production, Horizon Theatre Company turns “ho ho ho” into “ha ha ha” as it reprises its popular production of “The Santaland Diaries” by award-winning satirist David Sedaris. The merry misanthrope, played by Harold M. Leaver, recounts the tale of an out-of-work writer working as a Macy’s department store elf named Crumpet. Besieged by bratty children with overzealous parents and donning a humiliating costume, Crumpet finds his cynical self and elfin alter ego are not exactly compatible.