(Strip Number 1270, Original Publication Date, 23 March 1988)
Panel 1: When 2:15 rolls around, John asks Elly if the Tooth Fairy has paid Lizzie a visit only to get grunted at.
Panel 2: When he asks if the grunt was affirmative, negative or undecided, she growls a little.
Panel 3: He then delights in the fact that the first grunt was an affirmative grunt.
Panel 4: He then guarantees that Elly will be awake until morning trying to decipher his crack about how you know that you've been married a long time when you start taking each other for grunted.
Summary: John's propensity to tell Dad jokes reminds me of what Batman told Joker in the Killing Joke: "It wasn't funny the first time!"