I Remember Mono shows that Peggy goes to West Arlen Highschool and plays on the girls softball team against the girls of Arlen Highschool (where Hank is a student). The episode opens with young Bobby making Valentine's Day preparations and poor Luanne becoming her own valentine.
In their teenage years, Hank and Peggy had to skip a Valentine's Day date together because Hank caught Mono. Back then, he told Peggy it came from accidentally sharing a beverage with one of his football buddies. The truth will be unveiled later in the episode and their marriage suffers a serious shake-up. After much explaining, Hank once again comes out virtuous and in control of the situation. Tune in for the laughs.