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."
And the "Roast Your Loved One" funeral bit that follows, with Rip Taylor, Steve Allen, Charlie Callas, Slappy White and Henny Youngman:
Steve Allen: That's okay, Harvey, don't get up.
Henny Youngman: Why do Jewish guys die before their wives? They want to! Why do Jewish divorces cost so much? They're worth it!
Slappy White: Harvey had his will imprinted on his cock. But his lawyer said it would not stand up in court.