We finally broke down - after years of soundclips ("Can you dig it?") and podcasts, we watched the ultimate Theme Gang movie, The Warriors (1979).
Our anti-heroes are the Coney Island teen gang, the Warriors. They go to all the way up to the Bronx to a meeting of the gangs: Cyrus, the leader of the Gramercy Riffs, wants the gangs to form a truce and take over New York. But after he gives the "Can you dig it" speech, he is shot, and the guys who did it accuse the Warriors. So they have to get back to Coney across the Bronx, Manhattan, and Brooklyn, with all gangs against them. And they are wearing their colors, so they can't even hide.
To be honest, they don't actually meet up with too many Theme Gangs. In case you don't follow Filmsack, Theme Gangs are criminal gangs that are way too into their theme. For example, there is actually a mime gang in The Warriors - complete with whiteface, striped shirts and berets. The most famous of these is the Baseball Furies, with full uniforms, dazzle camo facepaint and bats as preferred weapons. The Warriors take them pretty easily. They don't have as much luck with the girl gang, the Lizzies.
This movie actually isn't as silly as you might expect from the late-70s hair styles. It's pretty gritty and the shots of a late-night deserted New York are pretty atmospheric. The references to the Anabasis add a nice touch of the mythic. However, it may be a little difficult to credit Michael Beck as a gang banger after you've seen him in Xanadu.