Fifth-worst flop of the decade: Cadillac XLR
13,302 (available 2003-2011)

What do get when you cross a Cadillac with a Corvette? Answer: Terrible sales.

Rolled out in 2003 as a 2004-model-year car, the XLR was basically a two-seat convertible Cadillac built atop a Corvette chassis.

General Motors ( GM) thought the XLR could make the stodgy Cadillac brand seem hip to a younger crowd, but the car proved neither luxurious enough for Cadillac fans nor sufficiently sporty for Corvette enthusiasts.

"I don't think Cadillac buyers were ever looking for that high a level of performance, so GM made the XLR a little softer and lower-power than a Corvette -- which meant the Corvette faithful didn't like the car, either," Takahashi says.

Besides, you could buy a fully loaded Corvette for about $20,000 less than the XLR's $75,000 price tag.

Takahashi says the car ultimately proved so unpopular that dealers needed until 2011 to unload the last of the XLRs, which GM had built for the 2009 model year.

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