Speaker burn in... I got to replace the tweeters and all the fuses in a brand-spankin' new pair of Maggies for one of our customers who read about burn-in and couldn't wait. He put on pink noise, cranked it as high as he could stand or a little higher, and left for the day. He brought them in for repair TWO DAYS after he took them home. My boss asked me to explain it to him. I struggled to find a way to not scream IMBECILE!!! and walk away, had to politely walk him through it.
Thinking back, he was one of those guys who bought into the super-cable fad, too. You know, $4/foot Fulton Gold... I still have a pair of those.