"There was a young lady from Venus, whose body was shaped like a--"
"The Naked Now" is an homage to the original series episode "The Naked Time." In it, the Enterprise crew is infected by a "virus" which removes an individual's inhibitions. It acts like intoxication. The episode does not delve deeply into sexuality but it does give us the most risque Star Trek scenes (up to this time).
In a rather infamous scene that has become a fan favourite we see Natasha Yar (Denise Crosby), under the influence of the virus, seduce Data (Brent Spiner). Data explains that he is "fully functional" and programmed for a wide variety of pleasuring. The couple engages in intercourse behind closed doors, and once the infection has been eradicated, Yar tells Data "It never happened." And although the incident is never again dealt with in any depth in season two's "The Measure of a Man," Data testifies in court that Yar was special to him and that they were "intimate."
In another scene, an infected Beverly Crusher (Gates McFadden), displays her strong attraction to Captain Picard (Patrick Stewart). Picard, also infected, struggles to reign in his attraction to Crusher.
In the pilot episode of the series we learned about these characters' history. Picard was a friend of Jack Crusher, Beverly's late husband. Picard was forced to give an order that led to Jack's death. This history serves to deepen the relationship between these characters as it unfolds and culminates in the series finale.
As one of the first few episodes of The Next Generation to air "The Naked Now" sets the stage for a brand new attitude toward sex and sexuality. 20 years have passed since the original series aired and society's views on sexual equality have changed drastically. Notice that in both of the incidents described above a woman is the sexual "aggressor". This is something not only new to Star Trek but relatively new to prime time American television in general.