No place, it seems, is ad free, not even a public toilet--now a venue for motion-activated talking posters. Catherine Moran of Lifetime Television, which has a 20-sec. plug for the reality show Cheerleader Nation airing in stalls in 15 cities, calls the "guerrilla" gambit "very intrusive--in a positive way." In fact, consumers say advertisers may be flushing away goodwill. Says Leia Jervert, who heard the ad four times in one restroom visit at a New York City pub: "I would prefer not to have my business solicited when I am doing my business."