That is unless it's likely to result in a collision.

I must assume the other guy is paying attention and knows the rules even though I know it's not necessarily the case. Once you start correcting even though you should stand on it complicates things and doesn't help teach rules of the road to the other guy. Of course, changing course 5 minutes ahead of a possible collision is just a course change.

If it gets close and I'm stand on I sound the horn, start screaming and shout obscenities at him.

That being said, commercial vessels, tugs and fishing boats are always the 'stand on' vessel and I stear clear. It's the clueless pleasure boater I like to screw with.

HEY! it can get boring out there and I'm usually the bigger vessel.