Alex P. Keaton: Mallory, someone stupid called... sometime today... about something trivial.
Mallory Keaton: Alex you know that could be any one of my friends.
When Alex mentions to Mallory that he's had sex before, he tells her he was 17 and that it was leap year. Not correct, this event occurred in 1982 (during one of the first episodes when Alex was 17), which was not a leap year.
Michael J. Fox wasn't the original choice to play Alex. Fox was cast after Matthew Broderick backed out, not wanting to commit to a TV series.