The guys on the center line are doing this to get attention, same as the loud pipes guys. I'm a long time bike rider and I know the type, nothing makes them happier than someone complaining about them.
When I ride in a group we ride staggered, not side by side. One guy is in the left tire track, then next guy in the right but a little behind. When we stop at a light we line up side by side to chat.
When I crashed my bike (must be 10 years now) I was glad that I didn't take anyone else down with me. And luckly it was hot, so I had removed my jacket, saved it from getting all covered with road rash and blood
