Fun thread, especially as someone who much prefers discussing negatives over positives. Atrium and lcd-5 are the ones for me, neither are bad but rather just not worth the price in the used market. "Disappointments" is an accurate term.
Lcd-5 is probably the least controversial take here, weird tonality and spatial presentation led to a headphone that sounded bizarre to say the least. Its resolution and mid-forwardness did lend itself for certain genres, but not for the ones I commonly listen to.
Atrium is an upgrade over the hd600, but not by much. Better resolution, soundstage, and bass detail, but worse vocals (yes, tried different pads) and too much bass quantity. Overall, too colored for me compared to hd600.
Not sure if iems are supposed to be included here, but most TOTL iems I demoed at canjam were disappointments, to the point I'm bascially done with iems. I did own the letshuoer cadenza 12, which I quickly sent back, as its sound was incoherent and unnatural.