My usual procedure at the diner is to run into the corner with the phone. I've only played TFN a couple of times, several months ago, but I don't remember the thugs being by the phone. But even if they were down there, it wouldn't change my tactics much.
If the thugs are near the entrance, I run to the phone area and immediately crouch so that they can't see me, although they shout and start to head my way. I buff up a little with whatever disciplines my current clan allows, and when they get close I rush out and start to attack with melee weapons. I go for the guy with the shotgun first, since he's the real danger. Then I kill the others, collect all of their weapons and head out. I've never really worried about the chef, but I never go near him either; so I guess my standard tactics keep the gunfire focused on me, not him. Maybe this is why I've never seen the cops unless I hang around too long.