Its usually pretty obvious that I'm using up the area that I'm fishing with boat movement, cast directions and so on. If someone still has to get into your cast zone then I would just try to strike up conversation. You can usually tell right off if someone is friendly or not. You never know, you may meet a new friend.
Don't be the one to be an azz, but if they insist on being rude I would probably just crank her up(with a good amount of time to warm motor up) and move on unless it was just such a great spot that you cant keep the fish off your line. Not many people want to stay right by you when your moving back and forth and slinging baits everywhere.
Getting too close to people seems unavoidable sometimes on busy lakes. Only other thing to do is stay off the water on the weekends. That's mostly what I do.

I was fishing a club tournament this past weekend on Sam Rayburn. Got to my spot right after sunrise, a cove about 120 yards across at the mouth and narrowed as you got deep into it ( i guess about 500 yards deep). I started at the point and had been there about 45 minutes before any other boats appeared. By this time I'm half way down the cove when another boat showed up. He stopped at the point and worked his way down the same way I was headed. The cove has now narrowed down to about 80 yards across where I was sitting fishing the hay grass. I was within casting distance to the back side of the grass. The other boat just kept coming down right where I was fishing so close I could cast to his boat. My back seater told him are you close enough, were fishing right here. The boaters reply was " your blocking the creek" and proceeded to go between us and the hay grass fishing all along? There was 50-60 yards to the grass on the other side. It was at that point I told my partner let's just go. I know what I did but would like to know how you would have handled this.

Its usually pretty obvious that I'm using up the area that I'm fishing with boat movement, cast directions and so on. If someone still has to get into your cast zone then I would just try to strike up conversation. You can usually tell right off if someone is friendly or not. You never know, you may meet a new friend.
Don't be the one to be an azz, but if they insist on being rude I would probably just crank her up(with a good amount of time to warm motor up) and move on unless it was just such a great spot that you cant keep the fish off your line. Not many people want to stay right by you when your moving back and forth and slinging baits everywhere.
Getting too close to people seems unavoidable sometimes on busy lakes. Only other thing to do is stay off the water on the weekends. That's mostly what I do.