Shawn quotes Pulp Fiction, "strikes down... with furious anger". Frank Whaley was in Pulp Fiction in the scene during that quote.
Pineapple reference: pineapple shaped bars can be seen in the window behind Lassiter while he is shooting in the shooting range.
This is the first episode of the series that Kirsten Nelson (Chief Vick) is not in.
Shawn tells Robert's ex-girlfriend, Amy, that one of the names considered for their gallery was "Night Gallery." This is a joking reference to Night Gallery, the 1970s television anthology series hosted by Rod Serling. The Night Gallery television series was produced by Universal Studios, the same company that produced Psych (and the movie Jaws, which is also mentioned in the episode).
In the scene where Shawn is now driving after drugging Gus, the song "Wake Me Up Before You Go-Go" by Wham! comes on the radio as Gus is waking up. This also relates because it says "before you go-go" when Gus did not want to go on a long drive and miss work.