All of David Alan Grier's bits as Don "No Soul" Simmons.
The extended Reefer Madness parody which airs during/after the final credits.
Mary: I didn't realize we had such specialized clinics here in Iowa!
Doctor: When science is on the march, nothing can stand in its way!
It's not so much that the Son of the Invisible Man fails to turn invisible, but that the rest of the jaded British bar crowd are playing along with the poor naked guy's madness and pretending he's invisible.
A guy watches two movie critics on television who suddenly start criticizing his real life, up to and including the "cliched heart-attack" that brings about his "predictable, boring death."