Comment by adsteel_

That's my memory as well. Early '00s, I was also in college and seemingly one year campus went from a broadly friendly, social place to one with a lot of people, headphones in, focused on their own little world.

There were Walkmans and disc Walkmans before that, of course, but MP3 players were a step change in social isolation, from my perspective. Bluetooth earbuds + a wave of streaming audio content have been another.