Now there are a few pet peeves I have with regard to riding bikes.
1) Not pointing out hazards on the road.
This one should be obvious. Road hazards are, by definition, hazards. Potholes, dead animals, large rocks, wood, people, etc. The list goes on and on and all it takes is a simple hand gesture. This is especially necessary in group rides. It's like using a turn signal while driving. Guess what? The turn signal stalk is there for a reason. It's super easy to use! (video NSFW)
2) Not taking a pull when you are active on the front of a group
Alright, first we must ask ourselves this one - extremely important - question: what is the POINT of a group ride? In my opinion (and keep in mind: this is just my own opinion) a group ride's point is to achieve the stated goals of the ride. Well, duh. Here are some goals:
Tuesday night ride @ IOS - Steady, fast paced group. Usually single paceline. Your turn comes on the front and you put the pedal to the metal. Separations can occur at various points along the route but generally it is just a high threshold ride around the airport.
Thursday "the Drop Ride" - 95% roadie group. As a consequence, this ride is ridden like a "roadie" ride. Frequent bursts at 120%+ as attacks occur and almost active recovery when nothing else is happening. The goal is to drop people or drop yourself.
Saturday/Sunday "group" rides w/ friends - Generally each person has intervals or if not, the goal to just hang on to those doing the intervals. Pretty simple.
Now, if I take a hard pull and move over to the left and wag my right elbow, that is the universal signal for the person behind you to take their turn. If you're on the front/near the front or you are responding to attacks by jumping on wheels then you should be willing to pull through. It doesn't matter if it's a pull to simply get back to the left. The WORST is when someone pulls out to the left behind the person on the front who pulls off to the left, automatically creating a gap to the person behind them and forcing that poor soul to cover two bike lengths during their move. Anyway, the heart of the matter is that if you're active on the front of a group you should be willing to pull through. No matter what.
Again, just my opinion.
One is a safety concern, one is an etiquette concern. Both are just my own; I do not know if these same things are important to others. I don't often (or ever) get my panties in a wad but I like to ride safe, I like to get my work in, and I like to have fun. Those are my goals on each and every ride I do.