Riding on the roof of the train. Not really possible in tunnels but dumb kids do it on elevated/outside trains. You can find videos on youtube of kids doing it. I know it was popular in NYC in like the 80s/90s or something, died out for a bit, and now seems to be having resurgence. And yes, kids have lost limbs and even died doing this.

I still can't believe that no one has found a video of this yet! Like did it actually exist or did we all just collectively hallucinate this catch phrase?

Doubtful. No other routes pass through there and I highly doubt that they're gonna put down new tracks to connect it to anywhere else. The only reason why it's on the Framingham/Worcester line is cause the tracks already passed through the area. All they did was add the new station to the existing line.