This latest Corn Productions show is not awful in the obvious ways: the acting and singing are competent, the dancing is simple but appropriately silly, and the costumes are sometimes quite funny. Instead these 80 minutes are painful because of the crass stupidity of the humor, as scenes inspired by faith and familiar holiday traditions are cause for an endless stream of sex jokes. There's no real point being made as baby Jesus hosts a gross Letterman-esque talk show, Charlie Brown gets frustrated by the pandenominationalism of Peanuts, or the coarse title characters enact an O. Henry adaptation that posits a pair of golden tit clamps as one of the duo's most valued possessions. Only audience members who'd revel in multiple gags involving butt plugs will find Tiff and Mom a ticket to holiday cheer. Through 12/17: Wed-Fri 8 PM. Cornservatory, 4210 N. Lincoln, 312-409-6435. $6-$12.