Panel 1: We start things off with Liz yelling "YUM!!!" and shocking Elly as she grabs one of the doughnuts she's sharing with Connie off of a serving plate.
Panel 2: We then remind ourselves of Elly's terrible parenting when she tells Elizabeth that she's magically supposed to know to ask first despite never having been told to do so. We also remind ourselves that Elly has just realized that Lizardbreath thinks that she can barge on in and take whatever she wants but does nothing about it but say that she knows things she doesn't know.
Panel 3: The strip proper begins with Liz making Elly feel uncomfortable by Pattersnarfing in front of Connie and thus destroying the illusion that she and the others don't regularly eat in a manner decreed to be barbarous by a select committee of Klingons. The Enjos aren't fooled so they're not close friends with most of the Pattersons.
Panel 4: It's Liz's turn to get gobsmacked when she's told that the table manners she was never specifically taught were awful.
Panel 5: Elly sets up the untranslatable punchline by telling a sullen Liz "How many times have I told you "DO NOT chew with your mouth open"?" because she can hear a dog-whistle that says "in front of company."
Panel 6: She then does that pious, I can't look at you thing when she tells Liz "DO NOT sit with your elbows on the table."
Panel 7: When Liz slouches and wipes her mouth on her sleeve, Elly tells her to do not do either.
Panel 8: When John makes the scene, he asks if he can join them. Liz says "Sure!"
Panel 9: When she says that they're having coffee and do-nots, he's confuses, Connie smirks and Elly is gobsmacked.
Summary: Elly wants to present herself as someone with manners but I remember things that she's at pains to avoid remembering. I remember a later strip that had her castigate Liz for bad table manners only to turn around and have worse manners when no one is looking. I also remember all the times we see her with a wodge of food in her cheeks as she talks about something. I even remember that Lizardbreath's primary reason for hating evil career women is being told where she can go and where she cannot.