As I've mentioned here before, Paramount did a nice little job of promoting one of their earlier properties, The Warriors, during a scene in Par's American Gigolo. Other than the same studio, there isn't much they share, save for both having watershed synth-based scores that remain awesome 30+ years later.
Recently, over at his Facebook feed, where he manages to unearth one cool vintage newspaper ad or marquee picture after another, Cinema Du Meep posted a December 1980 ad featuring--you guessed it -Warriors and Gigolo on the same bill. Curiously, Warriors, the earlier film by a year, appears as the first feature.
This was actually a traveling double-bill put together by Paramount and which opened simultaneously at several local theaters, as you can see in the below New York listing.
In this old thread on the Warriors website, posters mention that the "VGV" ("Varrio Grande Vista") graffiti on the Warriors sign above is the tag of a gang portrayed in the LA-set 1979 gang feature Boulevard Nights, which you can see here. So, it appears there was a little East Coast / West Coast rivalry which pre-dates Biggie and 2Pac.