[KingofWisdom]

Not counting Skullcandy ear buds or random headsets from Best Buy, I'd say Samson SR950s. They sound fine for the price, it's just everything beyond the sound quality that I can't stand. The ear pads (make too much noise), the design (uncomfortable self-adjusting headband that won't stay in place), the clamping force (can quickly cause a headache and these suckers HURT the ears). They feel cheap, like you'd be lucky to have them around after a year or two's use. These are the first headphones I bought where my reaction was "Nope! Can I return these?"

 

[TeskR]

Logitech G35 7.1 headset a few years back, really wasn't a comfortable headset.

 

[astroid]

Sony mdr 710 i think, they coiled into a wee ball. They were awful , whole parts of songs were missing or distorted.

 

[sealykojac]

I bought a pair of Beats Solo HD headphones from BestBuy with rewards points a few months back. I wanted to see if they were as bad as everyone claims. They were truly horrible and surprisingly lacking in the bass department. Luckily Amazon took them on trade for $8 less than I paid for them so it was a perfect swap of BB credit for Amazon credit.

 

[TWerk]

1) Sennheiser IE8- Lost it for awhile, eventually found it in my job's parking lot, clearly run over by someone. I didn't even care cause they sucked.
 
2) Grado 325i- Ugh. 

 
3) Skullcandy Skullcrushers- Hold on, let me get my double A batteries so this thing can vibrate on my head and call itself bass.

 

[bigeye135]

My old school had these headphones hooked up in the library and lab to all the computers.  Not only do they sound terrible, but they cause literal pain as your ears sit right up against the scratchy plastic.

 

[KlarkKentThe3rd]

Sony MDRZX100

 
I paid ~25$ for them. Apple earbuds sound better.

 

[Dragonzeanse]

Okay, so maybe it's not entirely fair to say they're the worst, because of their low price relative to the other things I own, but the Sony MDR-EX37Bs are pretty bad. Do you like sibilance? Do you wish you had a pair of headphones solely for the sake of listening to sibilance? Those are the IEMs you're searching for. They are so offensively sibilant that even less sensitive ears would feel exhausted listening to them. Wouldn't recommend them even at their current price.
 
Considering I don't tend to go out of my way to buy bad headphones, I haven't really owned any I'd argue are genuinely bad except the aforementioned Sony IEMs. I've used bad ones, though.

 

[BucketInABucket]

 

Sony MDRZX100

 
I paid ~25$ for them. Apple earbuds sound better.

Try modding them. They sound much better afterwards.

 

[KlarkKentThe3rd]

  Try modding them. They sound much better afterwards.

If a headphone requires modding, then you (or I) should have bought a better model in the first place.

 

[ricksome]

 
If a headphone requires modding, then you (or I) should have bought a better model in the first place.

Have to disagree with that. Many people buy Grado's or Fostex with the sole purpose of modding. The proof is right here on Head Fi

 

[TWerk]

 
Have to disagree with that. Many people buy Grado's or Fostex with the sole purpose of modding. The proof is right here on Head Fi

 
Indeed. For example, pad mods can make a big difference to sound. Once I put Alpha pads on my D2000, I really loved them. The mod made them sound better and become even more comfortable. 
 
With many other headphones, you can mod the pads and see major changes, sometimes for the better. When I had a pair of Grados, I bought the yellow sennheiser pads and really enjoyed them with those. I've heard for the M-Audio Q40, beyer pads can make a nice improvement to sound. There are numerous examples, but the point is headphones can be easily modded for the better.

 

[TWerk]

 
If a headphone requires modding, then you (or I) should have bought a better model in the first place.

 
Also look at the Mad Dogs. They are a mod of a cheaper Fostex headphone, with a huge following. The success of them clearly shows headphones can be modded to be better!

 

[GeneraI]

   
Also look at the Mad Dogs. They are a mod of a cheaper Fostex headphone, with a huge following. The success of them clearly shows headphones can be modded to be better!

As a recent owner of the mad dog 3.2's, I can confirm that modding a headphone can show the full potential of a headphone. 
Just bought an Asgard 2, so things can only get better from here. 

 

[KlarkKentThe3rd]

   
Also look at the Mad Dogs. They are a mod of a cheaper Fostex headphone, with a huge following. The success of them clearly shows headphones can be modded to be better!

Unfortunately, I don't have the technical skills. That, and modding does not change the fact that the driver will still be the same.