WordNet (r) 3.0 (2006):

laugh at
    v 1: subject to laughter or ridicule; "The satirists ridiculed
         the plans for a new opera house"; "The students poked fun
         at the inexperienced teacher"; "His former students roasted
         the professor at his 60th birthday" [syn: ridicule,
         roast, guy, blackguard, laugh at, jest at, rib,
         make fun, poke fun]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "laugh at":
   deride, despise, disdain, disregard, flout, grin at,
   hold in derision, laugh to scorn, make fun of, make game of,
   make merry with, pan, pillory, point at, poke fun at, put one on,
   rag, razz, ride, ridicule, roast, scoff at, scorn, scout,
   set at defiance, slight, slight over, smile at, snicker at,
   snigger at, treat with contempt