Back in 2007, I accidentally left my HD650s in a spot, that was easily reachable by my samoyed puppy. When I came back home, I found them totally wrecked and chewed up, he had stripped them bare of the soft velour pads. He probably didn't enjoy the rest very much, since it was all plastic, but man, when I saw the end result, I felt like I was gonna pass out.
I was in a tough financial spot right at that time, so I wasn't instantly able to afford another pair of HD650, so I bought.... HD590 I believe. The difference was, like, huge - at first I thought they were OK-ish, enough to get me through a month or two, till I could buy HD650 again.
Boy, was I wrong. With each passing day, the differences were gradually becoming more and more apparent, and I was getting more and more annoyed, instead of what I was expecting to happen - me adapting to the new headphones and starting to ignore the massive performance gap. Didn't even last a week, I think.
I wanted to grab HD580 instead, but they were already discontinued at that time.