If the Sole Survivor tells Waitron that they would like a table, he will escort them to the open booth and, once you sit down, he proceed ask you how one would like to be served. There are four options: mashed, diced, charbroiled, or if a speech check is pressed, one can tell him they are not hungry. If any of the first three options are or selected, or the speech check if failed, Waitron and Cook Handy will become hostile and attack. At this point it seems that one can defend themselves 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 them yet, and both him and Cook Handy will become hostile and attack. At this point it seems that one can defend themselves 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".