Without any signage at what you are calling the merge, the rider who first gets there has the right of way. Angry cyclist should have been pissed at himself for not beating you to it. There was a time when I would have engaged someone like that right off the bat. I am getting older now though, so I let stuff slide. As persistent as that jackwipe was, I may not have been able to abstain. I may have just turned and gone in the opposite direction for a while. Good on you for not escalating.

Around here it's pretty much MUPs or nothing. I have seen some remarkably stupid stuff on the part of walkers, runners and cyclists. I slow way down when I pass people on foot from behind. If they are well off to the side, I ease around without saying anything. If they are tending toward my side, I announce "I am coming around YOUR left" I don't yell it as I don't want to startle anyone. If they are wearing buds and don't hear me (which most are) I slip quietly by. If they acknowledge me "I say thank you enjoy your walk." as a slip by. Our MUTs extend into some remote areas where you can spin up a good pace. You simply must be prepared to slow, stop and yield to oblivious users when you encounter them though.