There are many ways to deal with it. Here are a few that I use and seem to work for me. I am not looking to make people angry and like you I just want them to stop sharking.
First I recognize that they are attempting to shark. This means that I can anticipate it. Knowing it is going to happen helps a lot because I do not get angry when the shark pulls his trick. The first few times I just stop what I am doing, wait a few seconds and then proceed. If that doesn’t work my next step is to simply stop what I am doing and stare at the person for 30 seconds or so (a long time). Everyone near the table knows why I stopped as I am looking at the shark for a long enough period of time that he and everyone knows why I have stopped playing.
Some people are just jerks and try to make like they were not attempting to shark. They try to cover their tracks, so to speak, and continue with some sort of comment. At that point I tell them that their talking while I am shooting is distracting and that when they have finished I will continue playing. I need not say that they are sharking. I make the statement that it bothers me to have someone do what they are doing. I make like it is my problem.
I have asked people to go and sit down, not to stand behind my shot, and to light their cigarette someplace else as needed. While I say that it is my problem it soon becomes obvious to everyone that it is the jerk who is a poor sport. Usually he quits, but not always. If it persists I just stop playing until the behavior goes away.
Remember that you are in control and that by simply highlighting his behavior and waiting until he quiets down he will make an ass of himself. That puts you back in control with a little satisfaction to boot, and you are still the good guy.
Works for me.
BTW I have noticed that after I have used these tactics some of the other players have picked up on it and have used similar behaviors to stop the shark attack. The shark wants to not only throw you off your game but make it look like you are not able to take the pressure as if you are the one who is less than a man. That is one way he covers his tracks. Recognize that, admit that it can throw you off your game and you defeat his attempts.