When Adam mentions that batman has shark repellent spray on his utility belt, it is a reference to Batman: the Movie. (1966)
Kevin Smith, an unapologetic stoner, directed this episode, which is season 4, episode 20. "420" is a number of great significance in the marijuana community.
This is the last episodes that Geoff is not in he is in every episode after this
Kevin Smith directed this episode revolving around the Batman (1989) movie. Kevin Smith such a comic book fan, he named his daughter Harley Quinn Smith. Harley Quinn is the girlfriend of the Joker, Batman's archenemy. Kevin Smith has also directed episodes of The Flash and Supergirl.
This episode is the first time we get a clear indication as to when 1980 something is. 1989.