Easily the 2007 Skoda Fabia 1.2 that I inherited.  I had no idea it was possible to hate an inanimate object so much. 
Horrible to drive with vague over-assisted steering and harsh, bouncy ride quality, weirdly placed pedals and back-breaking seats. 
It drank petrol and broke down repeatedly with niggly electrical and sensor issues and cost me a fortune. Just when it was finally behaving itself, the engine starting burning ridiculous amounts of oil and the mileage wasn't that high. Somehow managed to be inferior to my Peugeot 205 in every way despite being designed 20 years later and despite being much bigger on the outside, it had less usable space on the inside.
My 205 was the best by far and will be returned to the road when funds permit some body work. They were great to drive and the suspension can deal with the undulating bog roads around here in a way very few other cars can. I covered about 170,000 in my ownership and it only let me down once when the fuel pump seized.
Saying that, I have grown to love my Yaris. Not very exciting to look at or to drive but superbly engineered in every way. It just lack an old Peugeot's magic carpet ride.