Here's the thing, a hitman wouldn't need to go to the bathroom first just to come out again to shoot Tony. Some people say it's an homage to the godfather; however, unlike the godfather where Michael was expected and knew he was going to be searched, a potential hitman in this case wouldn't need to over complicate it. He's walk in and shoot him in the face. Not dick around at the bar watching him chit chat with his family and then go to the bathroom. What for? What need? he doesn't have a gun hidden back there like Michael Corleone.
This is a very good point. Michael Corleone gets a gun from the bathroom because he knew that he would be searched so he couldn't have a weapon on him. A hitman who was just going to casually enter and whack Tony could have shot him as he walked up, although to commit a murder in a restaurant full of witnesses? Even by Sopranos standards that's pretty ridiculous.
The scene is filmed in the most ominous way intentionally. Chase is illustrating the tension and pressure Tony will have to LIVE with for the rest of his life. We were suspicious of every single person who walks in that door, men who look like people who've tried to kill Tony and vice versa.
This is my thought as well. The constant shots of people entering (done as though to be from Tony's POV) is deliberate to show the underlying tension. Everyone could be a threat, or could be nothing. It's paranoia at its finest; even a dinner with his family is cause to worry, because who knows if the guy that just walked in has a gun and is ready to shoot you, or the person that seems to be listening just a little too closely to what you say is a FBI agent, or if that car that slows down is preparing to do a drive-by. In Season 1 Episode 4 after his mock execution, Christopher is all paranoid with Adriana and tells her, when she mentions that nobody followed her, that "[She] wouldn't know it if they did" and "It could be anybody, any time". That's what Tony has to live with.
