The one component that you wish you had not bought

McIntosh MVP-871, bought as a demo unit at Magnolia A/V. It never worked right despite two trips to their repair facility. McIntosh had refused to offer any warranty as it was too long out of production. I see McIntosh universal players for sale often for substantial discounts to MSRP. When I inquire why, I usually find that they have been repaired/refurbished by McIntosh. Don't get me wrong, I like McIntosh but they don't seem to have perfected their players to the same degree as many of their otherwise fine products. 

VPI PLC  (aka imo - complicated light dimmer switch)

I can't believe even today I still see these things for sale at $250.  

I'm with Mr. Tracy, saved up my pennies ,at a time I didn't have many, to buy a Crown IC-150.
After about a week reality set in and I realized my little Sansui 40watt integrated was VASTLY better !

My Meridian surround sound system, with processor, separate amp, and dsp speakers. I could never get it to sound nearly as good as my 2 channel system. I got better results with a Marantz receiver and non-Meridian speakers, at 10% of the cost. I will never go down the high end home theater rabbit hole again. Depreciation with HT components is much worse than quality 2 channel components.

Oh and I almost forgot my Supratek Syrah! Read all the online hype and what an epic piece of crap, I was rid of it within a week. Poor build quality and didn't sound great either.