Slap his/her hand away with a merry laugh and a "No! Silly sow, dick is for the fit." Keep it light, keep your cool. Laugh in their face and accentuate what a needy mess they're being. That way it's deniable if the porker runs to the bouncers claiming harassment out of spite.  If the problem persists, then find a better club; life's too short to be molested by sloppy drunk truffle beasts.