Love this one.
The easiest and most polite way of moving on that I have found is to simply say "I am glad that you have found a way that works for you, I want to give this routine/exercise (meaning the thing you are doing) a go and see how how I respond, thanks."
If you want to go a bit more technical you might say something like "I am following the advice found in Starting Strength (or quote some other source) and I am happy with the results I am getting with this method right now"
If somebody just can't get the hint and you want to essentially draw a line in the sand you can say "unless you can do more weight than I am doing with the same form I am not really interested in your opinion", the person will likely not talk to you again but there will be that weird friction in the gym for a while (which you might enjoy).
Finally if you just want to blow somebody's mind say "you know, I totally agree with you, but I am following what this douche-bag on T-Nation, Tim Henriques, says because I want to hurt myself to prove that he is wrong." See what they say to that. Odds are they will nod briefly and quickly walk away backwards, mumbling something nonsensical in the process.
The good news is that when you get really strong, or if you start training with a group of similar minded individuals, pretty much no one approaches you then.
Good luck with it