how sad; this is where common sense and halacha leave a gap apparently. the jewish nation is supposed to set an example by their behavior, and the one thing we must avoid at ALL costs is chillul hashem. so if one is a respected and well loved member of a community, and by saying a line about idols needing toilets he will cause some irritation, but not more than that, well i dont know maybe its ok.
but now imagine that saying that to a woman in a nail salon with whom you have no realtionship will cause her to be angry at your mockery of her belief (i am not saying this will happen, we have not been provided with enough information, i am merely wondering aloud to all those who blindly promote mocking idol worship) now she and all her co-workers go home and, fuming, tell all their families angrily about the rude jews who have no respect for others. well i wont draw up any crazy fantasies, but things could easily go beyond this point.
however, even without going farther, are you SURE that this behavior is what hashem desires? avraham avinu is not a good example; he was trying to accomplish something very different, and indeed had his own unique mission. NO ONE believed in god, and he needed to break through their belief system in a dramatic way. (according to many mefarhsim, not only was he was not aware god was going to perform a miracle for him, but he was actually quite certain that breaking all the idols like he did would result in his death. if mocking the idol worship in the nail salon would result in you being murdered, would you still be confident it was what hashem wanted?)
i would take a more appropriate example from the nun at rav yaakov kaminetskys levaya.