For me it has to be a Citroen C3 hire car on holiday, first hire car ever.
Absolutely rubbish - engine was tiny, gutless and barely got up the hills, no steering feedback, nothing. Didnt dare test it out properly...
Oh, and it only had 40,000km and the interior was trashed - "Silver" plastic parts were worn through to the black plastic underneath, gearstick numbers had almost gone - just a heap of junk all round.
I'd never buy a Citroen, and positively insist on hire cars *not* being a Citroen now.