You were out enjoying your ride in your own way, they cut you up as you describe it and IMO you were quite right to be annoyed tell then to fxxx off. They don`t own the road, no matter how faster / better ?? riders they may have been. Bunch of idiots
Actually, I feel a bit more charitable towards them. I'm not really looking to apportion (or accept) blame, I'm mainly interested in working out what's the best way to act in such circumstances - as much for safety reasons as anything else. Could I have done anything different that would have mitigated the situation? When you crash, it doesn't matter whose fault it is, it still hurts just the same. Best avoid it if possible.
LWaB's comments have been particularly enlightening - it's good to understand why these situations arise and benefit from the greater experience of other riders. I know my own limitations as a rider (in group situations especially - I've never been a racer - which is part of the reason I often prefer to ride alone). I suspect that cyclists are just the same as motorists, in that the more experienced you are, the more likely you are to have picked up bad habits. The second group that passed me were riding in the way they were used to, which may not have been entirely appropriate for the situation but I don't think it was especially dangerous, they just didn't account for me not riding in the same way as them.
I don't feel any particular ill will towards the rider who told me to fuck off either - I don't think he actually did anything wrong, if anything it was other members of his group who were to blame for the situation rather than him. But actually I'd rather not have fallen out with him at all. It would have been more helpful to both of us if we'd been able to discuss the incident in a more civil manner.
Tbh, I encountered much worse riding on the closed-road sportive I did in Scotland back in May.