To the OP: one thing is that once you're used to riding in groups, you get very comfortable with being inches from cyclists all around you. I have pissed off people on my local MUP by passing them with a couple of feet to spare (with bell warning) because they felt I was much too close. I felt I was giving them more than enough room. I need to remind myself that other people may not be used to bikes passing right by them and give extra room. Not saying the people passing you were excused at all, just trying to provide a little context.

Also, nothing drives me more crazy than people I'm riding with blowing through stop signs and red lights. It's inconsiderate, pisses drivers off needlessly, tars me (as someone riding with these guys) as a "one of those" cyclists and is really dangerous. I've actually had a group of guys I was riding with yell at me when I was pulling because I started braking for a red light. They essentially forced me to blow through the light.