Why did 90s movies struggle so much with accurately portraying teens?

I had just graduated high school when this movie came out and I can honestly remember watching it and thinking to myself, "do people really think this is what kids are like?" Actually, almost every 90s movie seemed like the writers/directors were trying way too hard to make kids look cooler than we really were.

I think, generally, this movie got some things right about teens of the time; the way they dressed, a few of the "groups" that people belonged to, etc. But, it was my experience that, even if kids fit in to one group more than another, they didn't just stick to that group only.

With that being said, what I found most obnoxious about teens in every 90s movie is the dialogue. 90s movies would often have one kid (Gavin, in this case) who spoke in long, descriptive sentences, using complex dialogue and big words that most kids never used. None of us talked like that. 90s movies never got the slang right either.

Poor Katie Holmes got the worst of the awful slang in this movie. Specifically, they had her using "razor" as a substitute for "cool" or "badass" etc.
When Gavin introduces Steve and Rachel: "Hey Rachel, wanna cruise town, have some beers?" "Sounds razor"...
When she and Steve are discussing Caldicott's past: "Hey Rachel, let's go to Bishop Flats and check out the mental hospital" "Razor. Let's go"...
When stopping for gas after running from the mental hospital: "The last ferry leaves at eleven thirty, just tell me you have a razor plan."

Stop trying to make Razor happen, Disturbing Behavior! It's not going to happen! :P

The assigning of random words that we didn't actually use for slang happened in a lot of movies back then and was particularly cringeworthy to me. Drove me crazy!
Some of Rachel's other gems: "Fail to be a tumor, Gavin" "What's your maladjustment, Effkin?!"

Any other movies you all can remember with such awesomely terrible 90s slang and/or teen portrayal attempts?