I think I'd go with Reality Bites, too, but honorable mention would go to Singles and Clerks.
You know, I've never seen Reality Bites. A while back on this board I made a case for Baz Lurhmann's Romeo + Juliet, reimagining a classic with a modern flair in the MTV Beachhouse style. But for some reason I also thought of Empire Records. I also just watched Airheads for the first time in years and it struck me as very 90s. Kids today probably don't even think about radio stations anymore.
What about the most 80s movie? WarGames? E.T.? Goonies? Breakfast Club?