Just joking, but me it was the 2002 Ford Explorer and its endless problems with the transmission, the wheels, the windows and everything else that could go wrong.
Just looking at carcomplaints can show you the size of the problem, with 1,500 reports of transmission problems alone.
My first car was a 1991 VW Fox. For it’s age it held up well, never leaked oil, but definitely had a decent set of issues. My favorites were loosing the linkage on my way to a breakfast date, and blowing my coolant hose up as I was arriving at the local sledding hill. Luckily there was a house next to the hill and the guy saw the smoke coming from under the hood and got us some duct tape to piece it together to get home, and I had water bottles in the back. Still my all time favorite car but I couldn’t get it to pass inspection because of the frame damage from the rust belt.
Briefly had a 2008 Subaru Impreza, but that’s my dads car now. Previous owner jumped it backwards and blew the TCU and destroyed the transmission. We swapped those out, which was the easiest swap I’ve ever done on a car; bar from dropping the transmission from the jack onto my hand. Last I heard my dad recently replaced the shocks on it.
My current car is a 2010 Jetta that has a massive oil leak, I just keep it topped up and 5 quarts of oil in my trunk, gotta be damage to the filter housing and I have a new one but I’ve put off doing it for like a year now. I also blew a tranny about a year after owning it, then I also lost the transmission in the car ;) (My dad hates this joke lol) The previous owners took it to AAMCO and the gear oil had been grossly underfilled. Swapped that out and it’s been running great since. In hindsight I should’ve done the filter housing at the same time as the transmission but I still thought it might’ve been the vacuum pump seal and replaced the gasket on that before learning it wasn’t. It was leaking a bit anyway so I’m glad I did.