if someone is fishing from a dock, leave it alone. otherwise it is fair game, and i dare say i would have kept fishing it even if the dude was yelling at me. if you're legal, tell them you know you're legal and if they have a problem then they can get the game warden.
i put people like this in the same category as theives. they want something for themselves that doesn't belong to them, and they think they can get it just by being an ass.
Oh, so you come along, fish under his private pier and the hard labor of building a under water structure over a long period of time, boat guy pulls up with his costas to catch fish and you're calling the pier owner a thief. What a loser you are to think that.