I don't know what the worst thing has ever been because people tend to say that stuff behind my back, rather than to my face. lol I suppose there's either some perverted form of respect in that, or else people just wouldn't dare voice their opinions when they know I have absolutely no interest in what their opinions are when it comes to what kind of parent I've always been.
What if someone had a comment to my face? If I were in mood to do this (rather than ignore it), and if I was angry enough to want to make the person feel like a stupid, clueless, worm (which I probably would be); I'd be polite and ask them to back up their statements and beliefs and reasoning. Then, because I know how careful, conscientious, and informed I've worked so hard to be (and because I know my own children and myself and my relationship with them better than anyone else in the world does), I would politely to point out all my own reasoning, information that I can back up in solid sources, experience, and anything else I had to back up what I think or do as a parent. And (forgive what will look like cockiness but is really just quiet confidence in knowing what I've always put into my choices/approaches as a parent) I'm fairly certain I would achieve my aim of making that person feel "like a nickel" (as my father used to say).
(See... This is why people know not to dare say anything to my face and instead live it in criticizing me behind my back - but that's OK. I don't have to deal with it. lol )
(Now if only I could figure out how to as effectively deal with people who mean well but seem to think they're "the boss of me" and treat me as if I'm stupid or else a kid. lol )