This one was mine, a 1998 Mercedes W208. The nice things about it were the cool Mono-Wiper, the engine (supercharged 2,3L M111) and the seats that were perfect for my height. It had a terrible ASR system but came with a LSD, so it was lots of fun in the winter.
The not-so-nice things about it were that the ignition randomly would not recognize the key, a missing catalytic converter, two fist sized rust holes in the front control arms, rust all over the underbody and the absolute worst 6-speed manual transmission I have ever used.
It also had multiple alignments but it didn't take long for the steering-wheel to be off-center again. You could see the tail end "crabbing" in the rear view mirror. There was something very wrong with it, which can probably be attributed to one of the 7 previous owners.
This isn't even counting all minor annoyances like the frameless windows not lowering themselves when you open the doors (that was only a thing after the 1999 model year), the wind noise, the awful interior materials, the broken seat latch in the rear, the trunk lock not working... I could go on for an hour like this.
So anyways, what is the worst car YOU have ever owned?
It was probably still worth what you bought it for. Those things hold their value forever, despite bring notorious for being unreliable.
I had a 93' with absolutely no features others than 4WD. No cruise, AC, nothing. It was worth about the same as my 05' accord with pretty much every feature.
The clutch died three times in 30k miles on my Wrangler. The local shop, a Jeep dealer, and a Wrangler specialty shop couldn't figure out why. I finally found the answer in a forum. Basically the brake lines shared fluid with the clutch and there was a small leak. The clutch always failed first so no one ever found the leak.
Also, the Wrangler is the only vehicle I've ever spun out on the highway, and it happened more than once.