Your opponent hits the ball into the rough and can’t find it. You stumble across the ball while looking for your own ball. Are you obligated to tell your opponent that you’ve found his ball, or is it “ok” to leave him in the dark, potentially costing him a lost-ball penalty?
The short answer: you’re allowed to remain mute by the rules of golf, but it’s a serious breach of etiquette to be such a jerk. Read more at about.com.