There are some people here in Brazil that express their regret on purchasing the car in a different way, like these:

This is a Chevrolet Vectra. It says on the rear windshield: "You will only understand when you have one. Vectra. A BOMB". Usually we call "bomb" something that is really a POS, like you say lemon. The Vectra's TV commercial used to say "Vectra, you will only understand when you have one".
Right above the rear badge it says: "You don't like your mother in law? Give her one of this"

On the front of the same car, it says: "Bought a dream, got a nightmare"
I also saw a Citroen Picasso with the following written on the rear windshield: "I HATE CITROEN"
I don't mean these cars are any bad "the vectra actually is", the main problem is when you have an issue with the car and the dealer doesn't seams to be interested in give any help.
There was a guy who had so much troubles with his brand new RAV4 that he made a website too. The engine was losing power, he took the car several times to the dealer and it end up replacing the engine, but the problem remained. The owner just asked for a new car cause he was really tired of all this s...t, then Toyota just sent a letter to him asking for 17K to replace the car...