The song playing at the start of the episode and end credits is "Monster Mash", a 1962 hit for Bobby "Boris" Pickett.
The porn movie that Krusty and Chief Wiggum saw (and the former being busted by the latter before "settling" it out of court), Debbie Does Springfield, is most likely named after the real life porn film Debbie Does Dallas.
The Valentine card Lisa gives to Ralph feature a train with a face which was similar to Thomas the Tank Engine.
Johnny's death in Skinner's flashback is a reference to Snake's death in the Metal Gear series when Colonel calls out latter's name 3 times when he's dead.
Johnny (the soldier who got shot while writing a Valentine's Day card to his girlfriend) sounds like The Squeaky-Voiced Teen.
Bart's off-color candy hearts read: "Luv Sux," "Prize Pig," "Kiss Off," and "Eat My Shorts".
Despite this episode airing in 1993, it actually takes place a year earlier due to Valentine's Day being on a weekday and Krusty having his 29th anniversary from 1963 (1992). As of February 19, 2013, it has actually been 50 years now.
This is the first episode to have a censor bleep.
Lisa erases another kid's name before re-signing and giving it to Ralph.
Lisa's romance with Ralph is referenced several times throughtout the series.
According to Al Jean, the "I Choo-Choo-Choose you" card is an actual valentine's day card he got in third grade.
Although George H. W. Bush was the president in 1992, Bill Clinton is shown as being the president in this episode.
Ralph spills chocolate ice cream on Lisa's dress, and according to Chief Wiggum, nothing can get chocolate out, but when Krusty is talking with Ralph on the audience,Lisa's dress is clean.
When Bart is pinpointing the second Ralph's heart broke in half, Ralph moves 10 times (10 frames) while Lisa moves only 5 times (5 frames). As they were in the same footage, they should have moved the same amount of frames.