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.
I bought my dad’s early 2000s Jeep Liberty off him for $1k. Every time I brought it to the mechanic, it cost another $1k to fix. The tow was extremely loose, so it felt like I was driving on ice. Hated it so much. Finally traded it in for a used Toyota RAV4.