Criticizing another persons picture when they haven't requested comment or criticism.
I did a lot of challenges years ago, to the point of winning some. It was a great learning experience. I eventually stopped, though, as it was clear that some entrants were low-balling their competitors to bring their averages down to get an edge.
Sometimes not even then. People have to be willing to hear the critique and to understand it. I find that almost as rare on DPR as the ability to actually construct a decent critique.
so you won't be singing the praises of Ken Rockwell photos then
I always find it odd, that out of the thousands upon thousands of famous, highly talented and influential photographers in the world, the only two photographers that get any regular mention in these forums, are Ken Rockwell and Peter Lik. And very occasionally, Ansel Adams.
That's incredible. I feel sorry for anyone who feels the need to behave like that. It's really nice to do well in a challenge but what price self respect?
Well, to be fair, we can't completely eliminate stupidity.
And on some occasions, they might even be right. 
I do too. That's the kind of creepo who steals dirty panites at laundromats.
Those are killer candids. Dope shots, Steve!
or someone with 82,000 posts on DPR criticizes an image you post claiming to be an expert .... when you ask them to post an example of their own illustrating the correct technique they refuse
This is fallacious reasoning. If you ask a mechanic what is wrong with your car, they can tell you without bringing in an example of one that isn't broken.
there is a famous saying :
Then you should have posted a picture demonstrating that.
