I've had it happen to me whilst fly-fishing and coarse fishing. Anglers will often appear from hundreds of yards away to fish on your shoulder once you start catching. To me etiquette is the mark of an angler.
I was pleasantly surprised the other day to hear a new, 17-year-old, member of our fishery ask a fellow angler if it was ok to fish near him - he was 20 yards away!
I once remember catching chub on the Derwent at Borrowash, near Derby. An angler approached on the far bank and fought his way through Hawthorn bushes to try and trot the same swim. He still couldn't trot the same line down the river and gave up after half an hour or so.
It was quite pathetic watching his attempts, he must have been ripped to shreds, but it was highly amusing to watch the lengths he was going to latch on to those fish