What’s your vote for the most ridiculous, overpriced, and useless tweak?

My vote: Furutech Outlet Cover 105 NCF $220, with “special crystalline material that has two “active” properties.” https://www.thecableco.com/outlet-cover-105-ncf.html

If you look at the first comment to the OP, it makes the very same point as yours. So here we are, 144 comments later, back to where we started.
Full circle, full stop.
cryogenically treating speaker cables. Back in around late '80's or early '90's cryoing rifle barrels was all the rage. Had one cryoed and it was 100 bucks pissed away. In spite of anecdotal evidence there is no proof that it does anything.
I cryo my rabbits before I smoke them. They are way better cryo'ed than not cryo'ed.
^^^ I tried smoking rabbits as a teenager. I found them hard to keep lit.
I have the Furutech demaganetizer (demag alpha). Anyone who listens to LPs or 45s, who doesn’t use one (or something equivalent) is only hearing maximum 90-95 percent of what’s on their records (varies per record). Subtract another 5% if you don’t use the Furutech SK-Filter.
As for PPT, all their stuff is just the best you can get.