just because its not marked no wake doesn't always mean its not, around here that means 500 feet from shore. (not sure how it applies in a section that's less than 1000 feet wide, and we have a lot of narrow waterways around my area, and most of them are either posted no wake, or "resume safe speed" which basically means WOT to me).
you can check your local ordinance's regarding the specific shoreline restrictions if any that would apply for you.
As far as to your specific situation, I don't believe any boater that's not under distress has the right to force you to do anything other than what your local regulations require, so you just can't "declare' a no wake zone when its convenient for you, although it might be respectful on your part to pass by in such a speed/distance as you wold like them to do if you were parked there...
I've had boaters that were fishing 10 feet outside the 25mph channel try to get me to slow down and frankly IMO its their stupid fault for deciding to drop a line 10feet outside the channel, I will go 25, but I'm not going slower to satisfy their needs.
If they wave at me I just wave back and keep going. If I get the 1 finger salute, It will just make me laugh and increase the chance that i'll give them the Maverick "buzz the tower" treatment on my return trip, although to be honest i've thought about doing that 20 times but really only done that once, and the jerk deserved it
when i'm in narrow waterways, like upper caloosahatchee, estero river, or kissimmee river, we slow down for boats/kayaks/fisherman routinely especially if they are not under power, and I hope that another boater would show the same respect if the situation was reversed.