How I Met Your Mother:
Season:     9     / Episode:     23    
Last Forever, Part 1

Ted waits around at a Halloween rooftop party at his apartment building for a girl dressed as a slutty pumpkin, whom he met at the same party four years before

Ted and Barney fly to Philadelphia after using one of Barney's techniques of picking up women. While in Philadelphia, the two end up doing something "legendary".

Ghostbusters is a comedy film franchise created in 1984. The two films center around a group of eccentric New York City parapsychologists who investigate and capture ghosts for a living. The first film was simply titled Ghostbusters, and was released on June 8, 1984 by Columbia Pictures. The film became a pop culture phenomenon, leading to a sequel, three animated television shows, a novel, a comic series, video games, a large number of action figures, a theme park attraction, and other merchandise.