In the scene in which the city is under immense peril after ignoring the Ghostbusters pleas to leave their system alone, the familiar face of a man more famous for showing off a different part of his anatomy can be very briefly glimpsed as part of a crowd scene.
Though the Ghostbusters theme tune video, recorded by Ray Parker Junior was packed with cameos, it was this appearance, by none other than adult film star Ron Jeremy that would be the crowning glory for some of the entire film. Reacting to the giant explosion, Jeremy can be seen displaying the same kind of acting skills that made him famous in his day job, though he thankfully does manage to negotiate the tough scene without resorting to humping the two older ladies standing immediately to his left.
Was Jeremy genuinely just walking past the set when he was taken over by the magic of the situation? Or was Ivan Reitman expressing his own personal appreciation of Ron's own body of work with this cheeky nod? My bet would go on the latter.