Oh just a few:
http://www.head-fi.org/t/278169/top-10-worst-headphones
http://www.head-fi.org/t/130195/worst-headphone-ever
http://www.head-fi.org/t/128858/what-are-the-worst-headphones-for-the-money
http://www.head-fi.org/t/400025/worst-headphones-ever
http://www.head-fi.org/t/571839/worst-headphone-you-ever-heard
http://www.head-fi.org/t/273413/worst-headphone-flops
http://www.head-fi.org/t/34067/worst-headphone-experience-ever
http://www.head-fi.org/t/31387/worst-headphones-ever-anyone
http://www.head-fi.org/t/24673/worst-headphones-ever
http://www.head-fi.org/t/518799/worst-headphones-you-ever-heard
http://www.head-fi.org/t/82102/worst-200-headphones
http://www.head-fi.org/t/31012/worst-looking-headphones
http://www.head-fi.org/t/315865/whats-the-worst-headphone-you-ever-bought
http://www.head-fi.org/t/477899/worst-headphones-above-100-300
http://www.head-fi.org/t/55256/worst-price-to-performance-headphone
http://www.head-fi.org/t/120966/what-headphone-is-the-worst-for-the-price
http://www.head-fi.org/t/430418/worst-headphones-youve-ever-heard-low-fi-experiences
http://www.head-fi.org/t/586289/competition-of-the-worst-sounding-headphone-for-its-price-bose-cough-monster-beat-cough
The word "worst" now looks and sounds incredibly weird to me...
And I'm not listing these as an "in your face" - I figure it's more fun to have all of those to read, than just the few pages you'll get of replies here.
As far as my contribution - the most terrible (I told you, the word just looks weird now!) headphones I've heard that actually exist within "high end headphone-dom" were probably the Ultrasone HFI-2400; they were just muddy and had no mids (everything was dominated by the midbass). They're better than a lot of the mainstream crap, I'm sure, but I haven't tried mainstream headphones in probably a decade (apart from Bose (which I would own if they were comfortable; guilty pleasure, I know), and a few minutes with one of the Beats models). I also didn't care too much for the Sennheiser 280, they're just too brittle and boring.
Quote:
By the way, I do believe there is another thread just like this.