I know what you're talking about. I had a guy who was twice my size this Monday night who kept standing at the pocket every time I tried to shoot and he'd either rock back and forth or swing his stick and talked about how I would miss a shot soon. He won the first two games, then I was able to block it out of my mind and kicked his butt a few times. After he lost 5 games in a row, he started getting much worse. Finally while I was looking over a full table hard cut shot, he stood behind the pocket rocking, shaking his stick, and then coughed when I started to pull the stick back. I stopped the stick, reset, and tried again, same result. So I simply stood up, looked at him and said, "I have been nice to you all night and sat on the stool while you shot. I'll wait to you can give the the same respect." He looked at me like a 5 year old and claimed his innocence. I told him I didn't care if he was doing anything on purpose but he was distracting me from behind the pocket and asked that he kindly move. He finally did and I made the shot. The VERY next shot he was behind the pocket again. I told him that if he was behind another poket I would be finished playing against him. He moved but was behind the pocket on the next shots till I finished on the 8 ball. After sinking the 8, I broke apart my stick, thanked him for playing me, and walked away.
The thing I think that kept me "safe" is that I never accused him of doing it on purpose. He couldn't get too mad at me because the problem was that I got distracted. However, I told him if he kept doing it I was done, and kept my promise. Sure, he could have broken a stick across my head, but I'd rather beat him, walk away, and let him know why. There are plenty of other people to play and plenty of other tables to play on.
On pay tables I have been known to let the guy win and then leave the bar. Again, plenty of other places to play a friendly game. At least tournaments prohibit people from doing this kind of BS.
Just my $0.02,
Chuck