Happened to me last Tuesday. I hit a drive to the dead center of the fairway, but its a blind shot. I play the course all of the time, so I know where I generally hit it distance wise. I walk up and there is a group just getting on the Tee box in front of us with no ball insight but my playing partner's. So, I walked over to the Tee and asked them if they saw my shot. Low and behold, I look down and the guy has my ball teed up and ready to play. I do the same thing and mark it very uniquely. I simply grabbed the ball off the tee and didn't say a word. He stared at me and asked me what I was doing. So I said, "Tell me how the ball is marked and what kind it is?" He tries to give me an answer that he obviously made up. I told him to play his own ball from now on. Needless to say it pissed me off for the rest of the round.