I have zero experience with group rides. If I were to give it a go with a group, I would appreciate someone explaining patiently to me how the groups work as well as the skills, techniques, manners and other ins and outs of group riding. I imagine I would also want to start out in one of the slower groups to learn these ropes. I assume there is a lead member responsible for making sure that new riders understand this. If not, IMHO, someone needs to take the lead to explain to this person how things are expected to work. If he is galled by this, kindly ask him to leave.
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"It is the unknown around the corner that turns my wheels." -- Heinz Stücke