While I don't doubt there are many inconsiderate people out there (and they're not unique to fishing either) I would like to comment that you might want to consider the individual may just not know any better when they crowd you, cast near you, walk right along the bank where you've been casting your dry fly to that riser for the past 20 minutes, etc. Not everyone has been brought up in a fishing family and has had manners and etiquette handed down to them by fathers, grandfathers, etc.

I'm a "late bloomer" when it comes to fly fishing and have only been doing it for 5 years or so. I grew up tossing worms, spinners and spoons in a local lake and pond for warm-water fish primarily bass, panfish and pike. Etiquette was just not crossing another guys lines. I remember the first time I went flyfishing in a "new spot" for me I had no idea what to expect. I worked my way along a path and finally arrived at a nice looking spot with a pretty run that looked like it might hold a couple trout. I eased myself into the water intent on not causing undue noise or ripples, all the while looking on where I was stepping for fear of falling in. I finally got into position and looked up to see I had entered < 100' upstream of another fisherman who was working the tail end of the same run. We both looked at each other and I knew I did something wrong. I apologized over and over. He began laughing (thankfully) and had no problem with me being where I was even though I probably sent a wave of mud down to him. We both proceeded to fish and I was rewarded with 3 nice browns out of that run.

My point is, I certainly didn't mean to enter the stream where I did if I knew it would disturb anyone and I'm guessing there are many out there who do something wrong albeit unintentionally. Perhaps a calm explanation of what the person did wrong might resolve the situation. I realize even a friendly explanation of what the person did wrong might escalate into an argument or worse but I doubt that's the norm as long as comments are civilized.

Just my .02 here ...