If you tell Waitron that you'd like a table, he will escort you to the open booth and, once you sit down, he will ask you how you'd like to be served. There are four options: mashed, diced, charbroiled, or you can pass a speech check and tell him you're not hungry. If you pick any of the first three options or fail the speech check, Waitron and Cook Handy will become hostile and attack you. At this point it seems that you can defend yourself without any repercussions.
If the player passes the speech check, the robots will continue to run the establishment. The next time the Sole Survivor takes a seat Waitron will sell various food items.
If the player leaves the booth without having been served, Waitron will call out that he hasn't served you yet, and both him and Cook Handy will become hostile and attack you. At this point it seems that you can defend yourself without any repercussions.
Upon entering the diner, Waitron will offer the Sole Survivor the last remaining booth. All of the other booths are occupied by skeletal remains which the player can ask about, Waitron simply refers to them as "satisfied customers".