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?
My first car was a rusty 72 Pinto. Objectively bad, but there's a freedom associated with a total shitbox as a 16yo that I've never had since.
Later had a mid-80s Cutlass Ciera. It already had an engine replaced by the time I got it, and that engine ran fine, unlike literally anything else in/on that car.
Briefly had a 77 F250. Also on a replacement engine, but this motor didn't last long. That beast only got like 9 MPG, so it wasn't worth fixing.
The 99 Jetta was fine for a few years, but when things started breaking, they broke in bunches. Finally a mechanic told me there was nothing he could do, so I had to scrap it.