Telepathy bomb causes the near extinction of the human race.
If there had been any journalists left behind (who cared), or news organizations left in tact after the bombs went off, that's what the headline might have read. But I'm not much of a writer, so that's what you get. Hell, at this point, we don't need journalists OR the news. We just listen, and there it is.
Apparently it takes a pretty strong mind to shut out the incessant noise of another person's brain, let alone the rest of the world's collective brains. Those who slaved away in their hot yoga classes benefited, as did much of the Eastern world. Various other people escaped the bombs with a terrible head ache and an instinctual ability to stop listening/seeing/whatevering. It took some time, and a lot of advil, but we managed.
I'm no scientist, so even with the vague knowledge I have of what happened that day, I can't explain it very well in writing. It was a form of chemical warfare; I know that much. It was intended to be something beneficial for humanity. No idea who thought it'd be a noble act to bomb the world with a barely-tested formula, but it happened, and I had other things to worry about.
Bombs were 'dropped' all over the world, and the condition is highly contagious. There are a few people left who aren't infected, but they've holed themselves away somewhere. In mountains, underground. We try not to know, but we have a general idea. They don't broadcast their thoughts like we do, uncontrollably, but if we listen for them, we hear their silent pleading to be left alone. So we leave them alone as best we can.
And that's the problem, really. Most of the population went insane when they couldn't stop hearing thoughts, or seeing images. The survivors learned how to stop listening, but we're pretty sure we never learned how to stop broadcasting.
At first, survivors converged to the same locations to be together. But we quickly discovered that knowing what someone thinks about you, if they know you, is really hard to handle. The brutal honesty that you weren't used to having someone else hear, that was all out on the table. Even if you didn't Listen to them... the temptation was always there. Many people drifted apart, content to seek communication telepathically if they were so inclined.
Sex sure became interesting, though. There were even a few of us who'd become pregnant since the incident... we wondered, what would happen to the babies? Would they be Listening in the womb? Be born full of the knowledge of the world? How awful.
Language isn't a barrier anymore, either, because if we can't understand the language, we can understand the conjured images pretty well.
Which is how we understood what the Valn were trying to communicate when they showed up. When we saw their ships in the sky, we all Listened, excitedly chattering at each other about the event. We tried to send them images of doves, olive branches, other stupid images of peace. It figures that the first time we'd come into contact with an alien race, it'd be because we were the loud, shitty neighbors. They politely asked us to shut up and stop polluting the universe with our incessant squawking. We hadn't even considered that anyone else could hear us. Humans really are inconsiderate assholes.