I am a fishing charter captain and diver. You should extend the same respect and courtesy to a person fishing as you would expect them to extend to a diver diving (you). In my experience, people who come too close to a diver or flag are ignorant. Most boaters don't know the marine saftey rules, never mind dive flag rules. The best thing you can do is to educate people courteously. When running our boat while drift diving and a fishing boat gets too close, we don't cut lines, etc. We educate. If you are cutting lines and being offensive you'll just convey nagativity and bad repuation against divers.
Most people are sorry for getting too close and will remember next time. Boaters who hassle you or get too close more than once should be reported by calling the local CG, etc and turning hull numbers in. It's never a good idea to take it into your own hands. Divers are no sensible match for boats and fishing gear.
Rules vary by state but generally:
Boaters must make reasonable efforts to stay 300 feet away from divers-down flags in open water and 100 feet away in rivers, inlets, and navigation channels. Boaters approaching flags closer than these distances must slow their boat to idle speed, or the minimum speed necessary to maintain forward motion and maneuverability.
Note that it's not REQUIRED. It's only reckless if a boat approaches above idle speed, and only then can a violation be issued. Unfortunately, most fishing is within this speed limit - and there are usually no enforceable rules pertainling to "fishing" near dive flags.
Also, the divers-down flag cannot be displayed in an area that would obstruct boat traffic or creates a hazard to navigation on any river, inlet, or channel, except in case of emergency.
So don't think boats HAVE to go around you. They don't. Use your judgement on your dive location.
Again, check the local state laws. These are just general rules.
Capt. Jeff Duncan