(Strip Number 226, Original Publication Date, 9 February 2011)
Panel 1: As John drives Will and Carrie to the airport, Mike, who's sitting in the back seat, marvels at the fact that Gran keeps calling him Johnny.
Panel 2: Carrie gets all affectionate as she reminds John that when he was little, she used to call him "Johnny Jump-up".
Panel 3: Mike starts laughing raucously; this irritates and alarms John.
Panel 4: John's Penetrating Death Glare™ causes Mike to say "And I'm not going to tell a soul, right?"
Summary: Why the need to not be laughed at, you ask? Simple! John and Elly are, as the Lynnsight will no doubt indicate, transfixed by the delusion that if their children laugh at them (or even see them laughing), they will lose all their credibility and be useless as parents.
ETA: The latest banner reminds us that eventually, John and Elly will look like clones of one another.