1982 VW Scirocco. Bought it from a car auction and the engine expired on the way home. Had it rebuilt, but it still ran like a dog. Brakes failed (twice), headlamps went dim when you switched the radio on.... leaked from the sunroof and tailgate...
In the end I swapped it with a more mechanically-minded mate for some stereo equipment. He fixed it up and kept it for 5 years. He sold it and then bought it back a few years later... it was his favourite car!
The most hateful car that I have ever had the misfortune to have to use was my ex's Metro... and absolute heap of sh1t. You could move the steering wheel a foot without the wheels turning. The seat collapsed once whilst she was driving at 60mph.