If an XXL turd floods forth from the toilet, do not back away in fear. That's the message in one of Weissman's tamer vignettes (''The Fecality of It All'') and good advice to anyone contemplating this raunchy collection of absurdist humor. The tales slalom from nymphomaniacal twins whose favorite movie is ''Shoah'' to a man fired because his massive organ is ruining office productivity. Along with a passion for orifice politics, defecation, and murder, Weissman is a ski fetishist: ''Headless'' opens with a story about Hitler's alpine dreams and downhills to a series of letters published by an imaginary magazine for people best described as snow-mosexuals. There are poignant moments as well, but most are buried under the avalanche of provocative vulgarity.