I havent ridden in a few years now but rode a lot for about 10 years. Every time this discussion comes up I think about the bad groups I hear about over on US1 and the idiots from Rev's town. But honestly, I have not really witnessed much the behavior everyone talks about. I see a lot of single riders who generally do a good job of staying to the right. Groups I see all seem to behave pretty well.
As a cyclist, I honestly cant think of many times where a double pace line made any sense in the real world. I have ridden them on some roads where the traffic was almost non-existent and it was safe to do but it was more fun than necessary. I guess if it were a very lightly travelled road and a very large group is cuts the length in half but when there are bike lanes, I honestly think single file in the bike lane is the way to go. If it is a large group that needs to double up, they should really stay away from high traffic areas. I say that as a cyclist.
As a motorist, I still say I have not seen very much of the poor behavior on the cyclist part at all. I have seen far more poor behavior on the part of the motorists. That is basically why I quit riding. Too many people texting or otherwise distracted. Too many impatient people who cant seem to deal with 4 seconds of delay on their way to the fast food drive through. Too many drivers with attitudes toward cyclists that I did nothing to cause.
One road rage story. I was riding in a group of about 8 guys. This was a very experienced group of riders, all over 40 and all very safe and considerate on the road. We came to the end of this road and were preparing to make a left. There are normally no cars at all back there so we had wandered into the left turn lane and were not in a hurry (it was right after a sprint). Well, on this day, a car was coming from behind and making the same left. We were in the wrong in that we were lollygagging a bit but didn't hold this guy up by more than a couple of seconds. No more than if there had been a car in front of him. Well, apparently that was more than he could stand. He screamed something out the window and layed on his horn while he sped around the corner. Normally this group would have laughed it off but one of the guys flipped him off as he was speeding away. He sees it and slams on the brakes and gets out of the car. As he got back to us, I think he realized he may have made a bad decision. I was the smallest guy in the group at 6'0" and 225lbs. He yelled some obscenities and got back in his car and sped away. What was funny was, his wife and daughter were in the car. Well, about 30 minutes later in the ride, he was coming back from where he went and was headed toward us. He floors it and comes into our lane from the opposite direction and runs us all off the road. And this was a road with very little shoulder and a guard rail, then canal. He had to be going 70mph. That could have been really ugly.
I guess my point is, I know there are douche cyclist out there but I dont think the bad behavior mentioned is as prevalent as good and definitely not as prevalent as bad driver behavior. So I dont get the hate either.