[FriedRice25]

AKG Q460...bought them on impulse because I liked the Q701 and didn't do my research. They did absolutely not impress me.

 

[asdfghjkzxcvbnm]

Pioneer HDJ-500, not so comfortable

 

[DarSevn]

Like a few other posters, I researched everything I bought beforehand so I am not really disappointed with any of my purchases.  The headphones getting the least amount of use though are my M50's.  They were the first decent pair I bought and I really enjoy the sound of them but everything else I have just wins out.  I bought Sennheiser 598's after the M50's, there is just no comparison.  Then I got a pair of Grado SR80i's and I found that I am in the category that enjoys the "Grado sound".  Then, I got a pair of Sony XB500's which I use exclusively for when I listen to hip hop/rap while gaming.
 
At least with the 4 pairs I have right now, I have a lot of variety in the sound so I never feel bored, and I have no reason to upgrade until I move on to the wallet breaking category of headphones.  My portable rig though, now that is something I have plenty of room to work on hah.  And on that note, I will grab my M50's and give them a good listening now, it's been a while.

 

[Baten]

I lost some money buying and quickly thereafter selling HD650's which is a bit of a shame. Then again, I did learn that I dislike "dark" sounding headphones and rather like lush mids and tilted (but not too harsh) treble, so I did learn a lot about my musical preferences.

 

[alucard177]

Denon D1100, I wanted some headphones with a strong bass... then I read about the terrible build quality problems they have. 

 

[cswann1]

For me it was the Beyer DT770  80ohm.  I was a hp newb at the time and at first listen I was so impressed with the bass (first closed HP for me) that I didn't notice how crappy everything else was.  A week later and I couldn't stand to listen to anything on them.

 

[takato14]

God... 
 
The AKG K240 Studio. Smooth and silky... and incredibly asleep sounding, there's practically no transients and the soundstaging is mediocre. These are generic loudness headphones masquerading as studio cans and are a disgrace to the AKG name. 
 
My uber-sh!tty Wal-Mart headphones from the mid 80's are better than these.

 

[GloryUprising]

V-Moda M100.
 
Couldn't resist the hype. I'm totally NOT a "V-Shaped" guy.

 

[IzzyAxel]

Sennheiser HD600, Grado RS2i, Beyerdynamic DT235, Audatron whatever whatever, and Sony MDR-F1, Fostex T50RP for me. (ATH M50 too, but the remorse came like, 3 years after the purchase when I realized they were horrid in every way)
 
HD600, how anyone can say these sound true to life is so far beyond me, it blows my god damn mind.  Started me on my path of distrust of subjective opinions and realizing objective measurements are not indicative of what a headphone sounds like to you.
 
RS2i...you'll like it if you like the way migraines feel.  Screechy, harsh, and resonant to hyperbole in the upper registers, these things physical hurt to listen to.
 
DT235 has no redeeming qualities...or so I thought until I tried the Audatrons, which actually don't.
 
F1, I don't remember the sound all that well, but not because it's been a while; because they broke within 4 hours of receiving them, and Sony couldn't repair them.  What I do remember is mellow and relaxing mids and treble, very weak bass, and meh soundstage with diffuse blurry imaging.  Not one I'm jonesing to try again.
 
T50RP, dark and sluggish, the drivers have awful transients, which is why I wonder why people praise these and the mods so much, since transients cannot be altered through modding the damping and enclosure.
 
All of these except the F1, I gave a fair shake to, and plenty of power.

 

[Eugguy]

For me, I have a few regrets...I would say the biggest purchase to disappointment value was the Sennheiser IE800. Next was the Denon D2000 and D5000. The Ultrasone Pro900 and DJ1Pro are next. The remorse I feel is due to the return in value I've received from each headphone. These have all been sold briefly after a long-detailed listening session. I feel that even though there is the "law of diminishing returns" always present in any high price purchase, there still has to be a base amount of value and enjoyment.

 

[wu wei]

The AKG K550 was the only set I was considering that I couldn't audition before purchasing. Between the positive reviews on S&V, Innerfidelity and Whathifi I figured they were worth the plunge for a good sealed can. I was wrong. They had virtually no low end. Female vocals sounded cold and grainy. The top end was revealing, but at the expense of midrange body and low end heft. I liked that I could hear the soloist's oboe keys opening shutting during Bryden Thomson's Vaughan William's Concerto for Oboe and Strings in A minor. I did not like that the oboe and the rest of the orchestra sounded like they were coming out of an AM radio.

 

[GloryUprising]

The AKG K550 was the only set I was considering that I couldn't audition before purchasing. Between the positive reviews on S&V, Innerfidelity and Whathifi I figured they were worth the plunge for a good sealed can. I was wrong. They had virtually no low end. Female vocals sounded cold and grainy. The top end was revealing, but at the expense of midrange body and low end heft. I liked that I could hear the soloist's oboe keys opening shutting during Bryden Thomson's Vaughan William's Concerto for Oboe and Strings in A minor. I did not like that the oboe and the rest of the orchestra sounded like they were coming out of an AM radio.

 
I actually thought the same thing; until I figured out how to get a proper seal.  A proper seal changes EVERYTHING about the k550.
 
Problem is a proper seal is very finicky and it kept unseating with the slightest movement. If you have a larger head I think it would sound wonderful.  In the end, I sold it too. 

 

[wu wei]

@GloryUprising
Yeah I fiddled and fiddled to no avail. If I pressed on the cups so that the drivers nearly touched my ears the sound improved tremendously. But of course I'm not going to do that for hours at a time! The search continues...

 

[Jetblack08]

Some will think that I am crazy but the se 535's are a disappointment. They were the first high end phones I purchased and for a time I thought they were great... then I purchased the W4...WAY better sound. After that I purchased the Sm3 v2... WAY better sound. I read some of the threads singing the praises of the se 535s and I revisit them from time to time and I always come to the same conclusion...they are no where near worth the price that they ask for them. It makes me hesitant to purchase the se 856s.

 

[BobG55]

3 expensive impulsive/compulsive headphone buys which I regretted & lost money on selling them :
 
1-) Sennheiser HD700 : I bought into the idea that they would be a scaled down HD800 without the sibilance; what they turned out to be was a harsh, unbalanced distorted sounding headphone.  Very disapointed especially with all the hype and how long it took for Sennheiser to put them on the market.  Save your money. 

 
2-) Grado RS1i : the hype about these HP was the detail and soundstage quality; I found them to be overly bright and the detail was nothing special.  They were ok but but way overpriced which is what made me dislike them even more in the end.

 
3-) The AKG K702 65th Annies : I have the K702 which I still like so I thought the Annies would be an improved version of the K702s; thank God I bought them 2nd hand & not full price because those HP sound muffled by which I mean the separation and balance of the sound is nothing like the prototype K702 & the extra bit of bass doesn't do anything to make them an improvement over the K702.  Whatever AKG had in mind for these HP it didn't pan out.
Sold them for close to the initial price I paid.